Ubuntu Manpage: DBD::ODBC - ODBC Driver for DBI

Provided by: libdbd-odbc-perl_1.45-1_amd64

NAME

       DBD::ODBC - ODBC Driver for DBI

VERSION

       This documentation refers to DBD::ODBC version 1.45.

WARNING

       Due to the discovery of a long standing unicode issue in DBD::ODBC the next development release (1.46_N)
       of DBD::ODBC is likely to exhibit a significant change in behaviour when retrieving CHAR/VARCHAR columns
       in a Unicode DBD::ODBC build. If you believe you have experienced any unicode issues with DBD::ODBC you
       are well advised to tell me now before it is too late.

SYNOPSIS

         use DBI;

         $dbh = DBI->connect('dbi:ODBC:DSN=mydsn', 'user', 'password');

       See DBI for more information.

DESCRIPTION

Change log and FAQs
Please note that the change log has been moved to DBD::ODBC::Changes. To access this documentation, use
"perldoc DBD::ODBC::Changes".

The FAQs have also moved to DBD::ODBC::FAQ.pm. To access the FAQs use "perldoc DBD::ODBC::FAQ".

Important note about the tests
DBD::ODBC is unlike most other DBDs in that it connects to literally dozens of possible ODBC Drivers. It
is practically impossible for me to test every one and so some tests may fail with some ODBC Drivers.
This does not mean DBD::ODBC will not work with your ODBC Driver but it is worth reporting any test
failures on rt.cpan.org or to the dbi-users mailing list.

DBI attribute handling
If a DBI defined attribute is not mentioned here it behaves as per the DBI specification.

ReadOnly (boolean)

DBI documents the "ReadOnly" attribute as being settable and retrievable on connection and statement
handles. In ODBC setting ReadOnly to true causes the connection attribute "SQL_ATTR_ACCESS_MODE" to be
set to "SQL_MODE_READ_ONLY" and setting it to false will set the access mode to "SQL_MODE_READ_WRITE"
(which is the default in ODBC).

Note: There is no equivalent of setting ReadOnly on a statement handle in ODBC.

Note: See ODBC documentation on "SQL_ATTR_ACCESS_MODE" as setting it to "SQL_MODE_READ_ONLY" does not
prevent your script from running updates or deletes; it is simply a hint to the driver/database that you
won't being doing updates.

This attribute requires DBI version 1.55 or better.

Private attributes common to connection and statement handles
odbc_ignore_named_placeholders

Use this if you have special needs (such as Oracle triggers, etc) where :new or :name mean something
special and are not just place holder names. You must then use ? for binding parameters. Example:

$dbh->{odbc_ignore_named_placeholders} = 1;
$dbh->do("create trigger foo as if :new.x <> :old.x then ... etc");

Without this, DBD::ODBC will think :new and :old are placeholders for binding and get confused.

odbc_default_bind_type

This value defaults to 0.

Older versions of DBD::ODBC assumed that the parameter binding type was 12 ("SQL_VARCHAR"). Newer
versions always attempt to call "SQLDescribeParam" to find the parameter types but if "SQLDescribeParam"
is unavailable DBD::ODBC falls back to a default bind type. The internal default bind type is
"SQL_VARCHAR" (for non-unicode build) and "SQL_WVARCHAR" (for a unicode build). If you set
"odbc_default_bind_type" to a value other than 0 you override the internal default.

N.B If you call the "bind_param" method with a SQL type this overrides everything else above.

odbc_force_bind_type

This value defaults to 0.

If set to anything other than 0 this will force bound parameters to be bound as this type and
"SQLDescribeParam" will not be used.

Older versions of DBD::ODBC assumed the parameter binding type was 12 ("SQL_VARCHAR") and newer versions
always attempt to call "SQLDescribeParam" to find the parameter types. If your driver supports
"SQLDescribeParam" and it succeeds it may still fail to describe the parameters accurately (MS SQL Server
sometimes does this with some SQL like select myfunc(?) where 1 = 1). Setting "odbc_force_bind_type" to
"SQL_VARCHAR" will force DBD::ODBC to bind all the parameters as "SQL_VARCHAR" and ignore
SQLDescribeParam.

Bare in mind that if you are inserting unicode data you probably want to use "SQL_WVARCHAR" and not
"SQL_VARCHAR".

As this attribute was created to work around buggy ODBC Drivers which support SQLDescribeParam but
describe the parameters incorrectly you are probably better specifying the bind type on the "bind_param"
call on a per statement level rather than blindly setting "odbc_force_bind_type" across a whole
connection.

N.B If you call the "bind_param" method with a SQL type this overrides everything else above.

odbc_force_rebind

This is to handle special cases, especially when using multiple result sets. Set this before execute to
"force" DBD::ODBC to re-obtain the result set's number of columns and column types for each execute.
Especially useful for calling stored procedures which may return different result sets each execute. The
only performance penalty is during execute(), but I didn't want to incur that penalty for all
circumstances. It is probably fairly rare that this occurs. This attribute will be automatically set
when multiple result sets are triggered. Most people shouldn't have to worry about this.

odbc_async_exec

Allow asynchronous execution of queries. This causes a spin-loop (with a small "sleep") until the ODBC
API being called is complete (i.e., while the ODBC API returns "SQL_STILL_EXECUTING"). This is useful,
however, if you want the error handling and asynchronous messages (see the "odbc_err_handler" and
t/20SQLServer.t for an example of this).

odbc_query_timeout

This allows you to change the ODBC query timeout (the ODBC statement attribute "SQL_ATTR_QUERY_TIMEOUT").
ODBC defines the query time out as the number of seconds to wait for a SQL statement to execute before
returning to the application. A value of 0 (the default) means there is no time out. Do not confuse this
with the ODBC attributes "SQL_ATTR_LOGIN_TIMEOUT" and "SQL_ATTR_CONNECTION_TIMEOUT". Add

{ odbc_query_timeout => 30 }

to your connect, set on the "dbh" before creating a statement or explicitly set it on your statement
handle. The odbc_query_timeout on a statement is inherited from the parent connection.

Note that internally DBD::ODBC only sets the query timeout if you set it explicitly and the default of 0
(no time out) is implemented by the ODBC driver and not DBD::ODBC.

Note that some ODBC drivers implement a maximum query timeout value and will limit timeouts set above
their maximum. You may see a warning if your time out is capped by the driver but there is currently no
way to retrieve the capped value back from the driver.

Note that some drivers may not support this attribute.

See t/20SqlServer.t for an example.

odbc_putdata_start

"odbc_putdata_start" defines the size at which DBD::ODBC uses "SQLPutData" and "SQLParamData" to send
larger objects to the database instead of simply binding them as normal with "SQLBindParameter". It is
mostly a placeholder for future changes allowing chunks of data to be sent to the database and there is
little reason for anyone to change it currently.

The default for odbc_putdata_start is 32768 because this value was hard-coded in DBD::ODBC until 1.16_1.

odbc_column_display_size

If you ODBC driver does not support the SQL_COLUMN_DISPLAY_SIZE and SQL_COLUMN_LENGTH attributes to
SQLColAtrributes then DBD::ODBC does not know how big the column might be. odbc_column_display_size sets
the default value for the column size when retrieving column data where the size cannot be determined.

The default for odbc_column_display_size is 2001 because this value was hard-coded in DBD::ODBC until
1.17_3.

odbc_utf8_on

Set this flag to treat all strings returned from the ODBC driver (except columns described as SQL_BINARY
or SQL_TIMESTAMP and its variations) as UTF-8 encoded. Some ODBC drivers (like Aster and maybe
PostgreSQL) return UTF-8 encoded data but do not support the SQLxxxW unicode API. Enabling this flag will
cause DBD::ODBC to treat driver returned data as UTF-8 encoded and it will be marked as such in Perl.

Do not confuse this with DBD::ODBC's unicode support. The "odbc_utf8_on" attribute only applies to non-
unicode enabled builds of DBD::ODBC.

odbc_old_unicode

Defaults to off. If set to true returns DBD::ODBC to the old unicode behavior in 1.29 and earlier. You
can also set this on the prepare method.

By default DBD::ODBC now binds all char columns as SQL_WCHARs meaning the driver is asked to return the
bound data as wide (Unicode) characters encoded in UCS2. So long as the driver supports the ODBC Unicode
API properly this should mean you get your data back correctly in Perl even if it is in a character set
(codepage) different from the one you are working in.

However, if you wrote code using DBD::ODBC 1.29 or earlier and knew DBD::ODBC bound varchar/longvarchar
columns as SQL_CHARs and decoded them yourself the new behaviour will adversely affect you (sorry). To
revert to the old behaviour set odbc_old_unicode to true.

You can also set this attribute in the attributes passed to the prepare method.

See the stackoverflow question at <http://stackoverflow.com/questions/5912082>, the RT at
<http://rt.cpan.org/Public/Bug/Display.html?id=67994> and lastly a small discussion on dbi-dev at
<http://www.nntp.perl.org/group/perl.dbi.dev/2011/05/msg6559.html>.

odbc_describe_parameters

Defaults to on. When set this allows DBD::ODBC to call SQLDescribeParam (if the driver supports it) to
retrieve information about any parameters.

When off/false DBD::ODBC will not call SQLDescribeParam and defaults to binding parameters as
SQL_CHAR/SQL_WCHAR depending on the build type.

You do not have to disable odbc_describe_parameters just because your driver does not support
SQLDescribeParam as DBD::ODBC will work this out at the start via SQLGetFunctions.

Note: disabling odbc_describe_parameters when your driver does support SQLDescribeParam may prevent
DBD::ODBC binding parameters for some column types properly.

You can also set this attribute in the attributes passed to the prepare method.

This attribute was added so someone moving from freeTDS (a driver which does not support
SQLDescribeParam) to a driver which does support SQLDescribeParam could do so without changing any Perl.
The situation was very specific since dates were being bound as dates when SQLDescribeParam was called
and chars without and the data format was not a supported date format.

Private methods common to connection and statement handles
odbc_getdiagrec

@diags = $handle->odbc_getdiagrec($record_number);

NOTE: This is an experimental method and may change.

Introduced in 1.34_3.

This is just a wrapper around the ODBC API SQLGetDiagRec. When a method on a connection or statement
handle fails if there are any ODBC diagnostics you can use this method to retrieve them. Records start at
1 and there may be more than 1. It returns an array containing the state, native and error message text
or an empty array if the requested diagnostic record does not exist. To get all diagnostics available
keep incrementing $record_number until odbc_getdiagrec returns an empty array.

All of the state, native and message text are already passed to DBI via its set_err method so this method
does not really tell you anything you cannot already get from DBI except when there is more than one
diagnostic.

You may find this useful in an error handler as you can get the ODBC diagnostics as they are and not how
DBD::ODBC was forced to fit them into the DBI's system.

NOTE: calling this method does not clear DBI's error values as usually happens.

odbc_getdiagfield

$diag = $handle->odbc_getdiagfield($record, $identifier);

NOTE: This is an experimental method and may change.

This is just a wrapper around the ODBC API SQLGetDiagField. When a method on a connection or statement
handle fails if there are any ODBC diagnostics you can use this method to retrieve the individual
diagnostic fields. As with "odbc_getdiagrec" records start at 1. The identifier is one of:

SQL_DIAG_CURSOR_ROW_COUNT
SQL_DIAG_DYNAMIC_FUNCTION
SQL_DIAG_DYNAMIC_FUNCTION_CODE
SQL_DIAG_NUMBER
SQL_DIAG_RETURNCODE
SQL_DIAG_ROW_COUNT
SQL_DIAG_CLASS_ORIGIN
SQL_DIAG_COLUMN_NUMBER
SQL_DIAG_CONNECTION_NAME
SQL_DIAG_MESSAGE_TEXT
SQL_DIAG_NATIVE
SQL_DIAG_ROW_NUMBER
SQL_DIAG_SERVER_NAME
SQL_DIAG_SQLSTATE
SQL_DIAG_SUBCLASS_ORIGIN

DBD::ODBC exports these constants as 'diags' e.g.,

use DBD::ODBC qw(:diags);

Of particular interest is SQL_DIAG_COLUMN_NUMBER as it will tell you which bound column or parameter is
in error (assuming your driver supports it). See params_in_error in the examples dir.

NOTE: calling this method does not clear DBI's error values as usually happens.

Private connection attributes
odbc_err_handler

NOTE: You might want to look at DBI's error handler before using the one in DBD::ODBC however, there are
subtle differences. DBD::ODBC's odbc_err_handler is called for error and informational diagnostics i.e.,
it is called when an ODBC call fails the SQL_SUCCEEDED macro which means the ODBC call returned SQL_ERROR
(-1) or SQL_SUCCESS_WITH_INFO \fIs0(1).

Allow error and informational diagnostics to be handled by the application. A call-back function
supplied by the application to handle or ignore messages.

The callback function receives four parameters: state (string), error (string), native error code
(number) and the status returned from the last ODBC API. The fourth argument was added in 1.30_7.

If the error handler returns 0, the error is ignored, otherwise the error is passed through the normal
DBI error handling. Note, if the status is SQL_SUCCESS_WITH_INFO this will not reach the DBI error
handler as it is not an error.

This can also be used for procedures under MS SQL Server (Sybase too, probably) to obtain messages from
system procedures such as DBCC. Check t/20SQLServer.t and t/10handler.t.

$dbh->{RaiseError} = 1;
sub err_handler {
($state, $msg, $native, $rc, $status) = @_;
if ($state = '12345')
return 0; # ignore this error
else
return 1; # propagate error
}
$dbh->{odbc_err_handler} = \&err_handler;
# do something to cause an error
$dbh->{odbc_err_handler} = undef; # cancel the handler

odbc_SQL_ROWSET_SIZE

Setting odbc_SQL_ROWSET_SIZE results in a call to SQLSetConnectAttr to set the ODBC SQL_ROWSET_SIZE
\fIs0(9) attribute to whatever value you set odbc_SQL_ROWSET_SIZE to.

The ODBC default for SQL_ROWSET_SIZE is 1.

Usually MS SQL Server does not support multiple active statements (MAS) i.e., you cannot have 2 or more
outstanding selects. You can set odbc_SQL_ROWSET_SIZE to 2 to persuade MS SQL Server to support multiple
active statements.

Setting SQL_ROWSET_SIZE usually only affects calls to SQLExtendedFetch but does allow MAS and as
DBD::ODBC does not use SQLExtendedFetch there should be no ill effects to DBD::ODBC.

Be careful with this attribute as once set to anything larger than 1 (the default) you must retrieve all
result-sets before the statement handle goes out of scope or you can upset the TDS protocol and this can
result in a hang. With DBI this is unlikely as DBI warns when a statement goes out of scope with
outstanding results.

NOTE: if you get an error saying "[Microsoft][ODBC SQL Server Driver]Invalid attribute/option identifier
(SQL-HY092)" when you set odbc_SQL_ROWSET_SIZE in the connect method you need to either a) upgrade to DBI
1.616 or above b) set odbc_SQL_ROWSET_SIZE after connect.

In versions of SQL Server 2005 and later see "Multiple Active Statements (MAS)" in the DBD::ODBC::FAQ
instead of using this attribute.

Thanks to Andrew Brown for the original patch.

DBD developer note: Here lies a bag of worms. Firstly, SQL_ROWSET_SIZE is an ODBC 2 attribute and is
usually a statement attribute not a connection attribute. However, in ODBC 2.0 you could set statement
attributes on a connection handle and it acted as a default for all subsequent statement handles created
under that connection handle. If you are using ODBC 3 the driver manager continues to map this call but
the ODBC Driver needs to act on it (the MS SQL Server driver still appears to but some other ODBC drivers
for MS SQL Server do not). Secondly, somewhere a long the line MS decided it was no longer valid to
retrieve the SQL_ROWSET_SIZE attribute from a connection handle in an ODBC 3 application (which DBD::ODBC
now is). In itself, this would not be a problem except for a minor bug in DBI which until release 1.616
mistakenly issued a FETCH on any attribute mentioned in the connect method call. As a result, it you use
a DBI prior to 1.616 and attempt to set odbc_SQL_ROWSET_SIZE in the connect method call, DBI issues a
FETCH on odbc_SQL_ROWSET_SIZE and the driver manager throws it out as an invalid attribute thus resulting
in an error. The only way around this (other than upgrading DBI) is to set odbc_SQL_ROWSET_SIZE AFTER the
call to connect. Thirdly, MS withdrew the SQLROWSETSIZE macro from the sql header files in MDAC 2.7 for
64 bit platforms i.e., SQLROWSETSIZE is not defined on 64 bit platforms from MDAC 2.7 as it is in a
"#ifdef win32" (see http://msdn.microsoft.com/en-us/library/ms716287%28v=vs.85%29.aspx). Setting
SQL_ROWSET_SIZE still seems to take effect on 64 bit platforms but you can no longer retrieve its value
from a connection handle (hence the issue above with DBI redundant FETCH).

odbc_exec_direct

Force DBD::ODBC to use "SQLExecDirect" instead of "SQLPrepare"/"SQLExecute".

There are drivers that only support "SQLExecDirect" and the DBD::ODBC do() override does not allow
returning result sets. Therefore, the way to do this now is to set the attribute odbc_exec_direct.

NOTE: You may also want to use this option if you are creating temporary objects (e.g., tables) in MS SQL
Server and for some reason cannot use the "do" method. see
<http://technet.microsoft.com/en-US/library/ms131667.aspx> which says Prepared statements cannot be used
to create temporary objects on SQL Server 2000 or later.... Without odbc_exec_direct, the temporary
object will disappear before you can use it.

There are currently two ways to get this:

$dbh->prepare($sql, { odbc_exec_direct => 1});

and

$dbh->{odbc_exec_direct} = 1;

NOTE: Even if you build DBD::ODBC with unicode support you can still not pass unicode strings to the
prepare method if you also set odbc_exec_direct. This is a restriction in this attribute which is
unavoidable.

odbc_SQL_DRIVER_ODBC_VER

This, while available via get_info() is captured here. I may get rid of this as I only used it for
debugging purposes.

odbc_cursortype

This allows multiple concurrent statements on SQL*Server. In your connect, add

{ odbc_cursortype => 2 }.

If you are using DBI > 1.41, you should also be able to use

{ odbc_cursortype => DBI::SQL_CURSOR_DYNAMIC }

instead. For example:

my $dbh = DBI->connect("dbi:ODBC:$DSN", $user, $pass,
{ RaiseError => 1, odbc_cursortype => 2});
my $sth = $dbh->prepare("one statement");
my $sth2 = $dbh->prepare("two statement");
$sth->execute;
my @row;
while (@row = $sth->fetchrow_array) {
$sth2->execute($row[0]);
}

See t/20SqlServer.t for an example.

In versions of SQL Server 2005 and later see "Multiple Active Statements (MAS)" in the DBD::ODBC::FAQ
instead of using this attribute.

odbc_has_unicode

A read-only attribute signifying whether DBD::ODBC was built with the C macro WITH_UNICODE or not. A
value of 1 indicates DBD::ODBC was built with WITH_UNICODE else the value returned is 0.

Building WITH_UNICODE affects columns and parameters which are SQL_C_WCHAR, SQL_WCHAR, SQL_WVARCHAR, and
SQL_WLONGVARCHAR, SQL, the connect method and a lot more. See "Unicode".

When odbc_has_unicode is 1, DBD::ODBC will:

bind columns the database declares as wide characters as SQL_Wxxx
This means that UNICODE data stored in these columns will be returned to Perl in UTF-8 and with the
UTF-8 flag set.

bind parameters the database declares as wide characters as SQL_Wxxx
Parameters bound where the database declares the parameter as being a wide character (or where the
parameter type is explicitly set to a wide type - SQL_Wxxx) can be UTF-8 in Perl and will be mapped
to UTF-16 before passing to the driver.

SQL SQL passed to the "prepare" or "do" methods which has the UTF-8 flag set will be converted to UTF-16
before being passed to the ODBC APIs "SQLPrepare" or "SQLExecDirect".

connection strings
Connection strings passed to the "connect" method will be converted to UTF-16 before being passed to
the ODBC API "SQLDriverConnectW". This happens irrespective of whether the UTF-8 flag is set on the
perl connect strings because unixODBC requires an application to call SQLDriverConnectW to indicate
it will be calling the wide ODBC APIs.

NOTE: You will need at least Perl 5.8.1 to use UNICODE with DBD::ODBC.

NOTE: Binding of unicode output parameters is coded but untested.

NOTE: When building DBD::ODBC on Windows ($^O eq 'MSWin32') the WITH_UNICODE macro is automatically
added. To disable specify -nou as an argument to Makefile.PL (e.g. "perl Makefile.PL -nou"). On non-
Windows platforms the WITH_UNICODE macro is not enabled by default and to enable you need to specify the
-u argument to Makefile.PL. Please bare in mind that some ODBC drivers do not support SQL_Wxxx columns or
parameters.

UNICODE support in ODBC Drivers differs considerably. Please read the README.unicode file for further
details.

odbc_out_connect_string

After calling the connect method this will be the ODBC driver's out connection string - see documentation
on SQLDriverConnect.

Typically, applications (like MS Access and many others) which build a connection string via dialogs and
possibly SQLBrowseConnect eventually end up with a successful ODBC connection to the ODBC driver and
database. The odbc_out_connect_string provides a string which you can pass to SQLDriverConnect (DBI's
connect prefixed with dbi:ODBC:") which will connect you to the same datasource at a later date. You may
also want to see "odbc_driver_complete".

odbc_version

This was added prior to the move to ODBC 3.x to allow the caller to "force" ODBC 3.0 compatibility. It's
probably not as useful now, but it allowed get_info and get_type_info to return correct/updated
information that ODBC 2.x didn't permit/provide. Since DBD::ODBC is now 3.x, this can be used to force
2.x behavior via something like: my

$dbh = DBI->connect("dbi:ODBC:$DSN", $user, $pass,
{ odbc_version =>2});

odbc_driver_complete

This attribute was added to DBD::ODBC in 1.32_2.

odbc_driver_complete is only relevant to the Windows operating system and will be ignored on other
platforms. It is off by default.

When set to a true value DBD::ODBC attempts to obtain a window handle and calls SQLDriverConnect with the
SQL_DRIVER_COMPLETE attribute instead of the normal SQL_DRIVER_NOPROMPT option. What this means is that
if the connection string does not describe sufficient attributes to enable the ODBC driver manager to
connect to a data source it will throw a dialogue allowing you to input the remaining attributes. Once
you ok that dialogue the ODBC Driver Manager will continue as if you specified those attributes in the
connection string. Once the connection is complete you may want to look at the odbc_out_connect_string
attribute to obtain a connection string you can use in the future to pass into the connect method without
prompting.

As a window handle is passed to SQLDriverConnect it also means the ODBC driver may throw a dialogue e.g.,
if your password has expired the MS SQL Server driver will often prompt for a new one.

An example is:

my $h = DBI->connect('dbi:ODBC:DRIVER={SQL Server}', "username", "password",
{odbc_driver_complete => 1});

As this only provides the driver and further attributes are required a dialogue will be thrown allowing
you to specify the SQL Server to connect to and possibly other attributes.

odbc_batch_size

Sets the batch size for execute_for_fetch which defaults to 10. Bare in mind the bigger you set this the
more memory DBD::ODBC will need to allocate when running execute_for_fetch and the memory required is
max_length_of_pn * odbc_batch_size * n_parameters.

odbc_array_operations

NOTE: this was briefly odbc_disable_array_operations in 1.35 and 1.36_1. I did warn it was experimental
and it turned out the default was too ambitious and it was a poor name anyway. Also the default was to
use array operations and now the default is the opposite.

If set to true DBD::ODBC uses its own internal execute_for_fetch instead of DBI's default
execute_for_fetch. The default is false. Using the internal execute_for_fetch should be quite a bit
faster when using arrays of parameters for insert/update/delete operations as batches of parameters are
sent to the database in one go. However, the required support in some ODBC drivers is a little sketchy
and there is no way for DBD::ODBC to ascertain this until it is too late.

Please read the documentation on execute_array and execute_for_fetch which details subtle differences in
DBD::ODBC's implementation compared with using DBI's default implementation. If these difference cause
you a problem you can set odbc_array_operations to false and DBD::ODBC will revert to DBI's
implementations of the array methods.

You can use the environment variable ODBC_DISABLE_ARRAY_OPERATIONS to switch array operations on/off too.
When set to 1 array operations are disabled. When not set the default is used (which currently is off).
When set to 0 array operations are used no matter what. I know this is slightly counter intuitive but
I've found it difficult to change the name (it got picked up and used in a few places very quickly).

odbc_taf_callback

NOTE: this is experimental until I at least see more than one ODBC driver which supports TAF.

Transparent Application Failover (TAF) is a feature in OCI that allows for clients to automatically
reconnect to an instance in the event of a failure of the instance. The reconnect happens automatically
from within the OCI (Oracle Call Interface) library.

TAF supports a callback function which once registered is called by the driver to let you know what is
happening and which allows you to a degree, to control how the failover is handled.

You need to set up TAF on your instance first and that process is beyond the scope of this document. Once
TAF is enabled you simply set "odbc_taf_callback" to a code reference which should look like this:

sub taf_handler {
my ($dbh, $event, $type) = @_;
# do something here
}

DBD::ODBC will pass the connection handle ($dbh), the Oracle event type (OCI_FO_END, OCI_FO_ABORT,
OCI_FO_REAUTH, OCI_FO_BEGIN, OCI_FO_ERROR) and the Oracle type (OCI_FO_NONE, OCI_FO_SESSION,
OCI_FO_SELECT, OCI_FO_TXNAL). Consult the Oracle documentation for what these are. You can import these
constants using the :taf export tag. If your instance is not TAF enabled it is likely an attempt to
register a callback will fail but this is driver dependent (all DBD::ODBC does is make a
SQLSetConnectAttr call and provide a C wrapper which calls your Perl subroutine).

Here is a commented example:

my $h = DBI->connect('dbi:ODBC:oracle','xxx','yyy',
{RaiseError => 1,
odbc_taf_callback => \&taf_handler}) or die "connect";
while (1) {
my $s = $h->selectall_arrayref(q/select 1 from dual/);
sleep 5;
}

sub taf_handler {
my ($dbh, $event, $type) = @_;

#print "taf_handler $dbh, $event, $type\n";

if ($event == OCI_FO_BEGIN) {
print "Instance unavailable, stand by\n";
print "Your TAF type is : ",
($type == OCI_FO_NONE ? "NONE" :
($type == OCI_FO_SESSION ? "SESSION" :
($type == OCI_FO_SELECT ? "SELECT" : "?"))) , "\n";
# start a counter and each time OCI_FO_ERROR is passed in we will
# count down and abort the failover when we hit 0.
$count = 10;
return 0;
} elsif ($event == OCI_FO_ERROR) {
# We get an OCI_FO_ERROR each time the failover fails
# sleep a while until the count hits 0
if (--$count < 1) {
print "Giving up\n";
return 0; # give up
} else {
print "Retrying...\n";
sleep 1;
return OCI_FO_RETRY; # tell Oracle to retry
}
} elsif ($event == OCI_FO_REAUTH) {
print "Failed over user. Resuming Services\n";
} elsif ($event == OCI_FO_END) {
print "Failover ended - resuming\n";
}
return 0;
}

NOTE: The above example is for use with the Easysoft Oracle ODBC Driver. ODBC does not define any
standard way of supporting TAF and so different drivers may use different connection attributes to set it
up or may even pass the callback different arguments. Unfortunately, I don't have access to any other
ODBC driver which supports TAF. Until I see others I cannot create a generic interface. I'll happily
accept patches for any other driver or if you send me a working copy of the driver and the documentation
I will add support for it.

odbc_trace_file

Specify the name and path to a file you want ODBC API trace information to be written to. See
"odbc_trace".

odbc_trace

Enable or disable ODBC API tracing. Set to 1 to enable and 0 to disable.

This calls SQLSetConnectAttr for SQL_ATTR_TRACE and either sets SQL_OPT_TRACE_ON or SQL_OPT_TRACE_OFF.
Enabling tracing will tell the ODBC driver manager to write and ODBC API trace to the file named with
"odbc_trace_file".

NOTE: If you don't set odbc_trace_file most ODBC Driver Managers write to a file called SQL.LOG in the
root directory (but this depends on the driver manager used).

NOTE: This tracing is produced by the ODBC Driver Manager and has nothing to do with DBD::ODBC other than
it should trace the ODBC calls DBD::ODBC makes i.e., DBD::ODBC is not responsible for the tracing
mechanism itself.

NOTE: Enabling tracing will probably slow your application down a lot. I'd definitely think twice about
it if in a production environment unless you are desperate as it tends to produce very large trace files
for short periods of ODBC activity.

Private statement attributes
odbc_more_results

Use this attribute to determine if there are more result sets available.

Any ODBC Driver which batches results or counts of inserts/updates will need you to loop on
odbc_more_results until there are no more results. e.g., if you are performing multiple selects in a
procedure or multiple inserts/updates/deletes then you will probably need to loop on odbc_more_results.

Use odbc_more_results as follows:

do {
my @row;
while (@row = $sth->fetchrow_array()) {
# do stuff here
}
} while ($sth->{odbc_more_results});

Note that with multiple result sets and output parameters (i.e,. using bind_param_inout), don't expect
output parameters to written to until ALL result sets have been retrieved.

Under the hood this attribute causes a call to the ODBC API SQLMoreResults and then any result set,
insert/update/delete or output parameters are described by DBD::ODBC and the statement handle will be
ready for processing the new result.

Private statement methods
odbc_rows

This method was added in 1.42_1.

In 64 bit ODBC SQLRowCount can return a 64bit value for the number of rows affected. Unfortunately, the
DBI DBD interface currently (at least until 1.622) defines execute as returning an int so values which
cannot fit in an int are truncated. See RT 81911.

From DBD::ODBC 1.42_1 DBD::ODBC

o defines this method which will return the affected rows in an IV (and IVs are guaranteed to be able to
hold a pointer) so you can get the real affected rows without truncation.

o if it detects an overflow in the execute method it will issue a warning (if Warn is on which it is by
default) and return INT_MAX.

At some stage DBI may change to fix the issue this works around.

NOTE: the return from odbc_rows is not the raw value returned by SQLRowCount. It is the same as execute
normally returns e.g., 0E0 (for 0), -1 for unknown and N for N rows affected where N > 0.

odbc_lob_read

$chrs_or_bytes_read = $sth->odbc_lob_read($column_no, \$lob, $length, \%attr);

Reads $length bytes from the lob at column $column_no returning the lob into $lob and the number of bytes
or characters read into $chrs_or_bytes_read. If an error occurs undef will be returned. When there is no
more data to be read 0 is returned.

NOTE: This is currently an experimental method and may change in the future e.g., it may support
automatic concatenation of the lob parts onto the end of the $lob with the addition of an extra flag or
destination offset as in DBI's undocumented blob_read.

The type the lob is retrieved as may be overridden in %attr using "TYPE => sql_type". %attr is optional
and if omitted defaults to SQL_C_BINARY for binary columns and SQL_C_CHAR/SQL_C_WCHAR for other column
types depending on whether DBD::ODBC is built with unicode support. $chrs_or_bytes_read will by the bytes
read when the column types SQL_C_CHAR or SQL_C_BINARY are used and characters read if the column type is
SQL_C_WCHAR.

When built with unicode support $length specifies the amount of buffer space to be used when retrieving
the lob data but as it is returned as SQLWCHAR characters this means you at most retrieve "$length/2"
characters. When those retrieved characters are encoded in UTF-8 for Perl, the $lob scalar may need to be
larger than $length so DBD::ODBC grows it appropriately.

You can retrieve a lob in chunks like this:

$sth->bind_col($column, undef, {TreatAsLOB=>1});
while(my $retrieved = $sth->odbc_lob_read($column, \my $data, $length)) {
print "retrieved=$retrieved lob_data=$data\n";
}

NOTE: to retrieve a lob like this you must first bind the lob column specifying BindAsLOB or DBD::ODBC
will 1) bind the column as normal and it will be subject to LongReadLen and b) fail odbc_lob_read.

NOTE: Some database engines and ODBC drivers do not allow you to retrieve columns out of order (e.g., MS
SQL Server unless you are using cursors). In those cases you must ensure the lob retrieved is the last
(or only) column in your select list.

NOTE: You can retrieve only part of a lob but you will probably have to call finish on the statement
handle before you do anything else with that statement. When only retrieving part of a large lob you
could see a small delay when you call finish as some protocols used by ODBC drivers send the lob down the
socket synchronously and there is no way to stop it (this means the ODBC driver needs to read all the lob
from the socket even though you never retrieved it all yourself).

NOTE: If your select contains multiple lobs you cannot read part of the first lob, the second lob then
return to the first lob. You must read all lobs in order and completely or read part of a lob and then do
no further calls to odbc_lob_read.

Private DBD::ODBC Functions
You use DBD::ODBC private functions like this:

$dbh->func(arg, private_function_name, @args);

GetInfo

This private function is now superceded by DBI's get_info method.

This function maps to the ODBC SQLGetInfo call and the argument should be a valid ODBC information type
(see ODBC specification). e.g.

$value = $dbh->func(6, 'GetInfo');

which returns the "SQL_DRIVER_NAME".

This function returns a scalar value, which can be a numeric or string value depending on the information
value requested.

GetTypeInfo

This private function is now superceded by DBI's type_info and type_info_all methods however as it is
used by those methods it still exists.

This function maps to the ODBC SQLGetTypeInfo API and the argument should be a SQL type number (e.g.
SQL_VARCHAR) or SQL_ALL_TYPES. SQLGetTypeInfo returns information about a data type supported by the data
source.

e.g.

use DBI qw(:sql_types);

$sth = $dbh->func(SQL_ALL_TYPES, GetTypeInfo);
DBI::dump_results($sth);

This function returns a DBI statement handle for the SQLGetTypeInfo result-set containing many columns of
type attributes (see ODBC specification).

NOTE: It is VERY important that the "use DBI" includes the "qw(:sql_types)" so that values like
SQL_VARCHAR are correctly interpreted. This "imports" the sql type names into the program's name space.
A very common mistake is to forget the "qw(:sql_types)" and obtain strange results.

GetFunctions

This function maps to the ODBC SQLGetFunctions API which returns information on whether a function is
supported by the ODBC driver.

The argument should be "SQL_API_ALL_FUNCTIONS" (0) for all functions or a valid ODBC function number
(e.g. "SQL_API_SQLDESCRIBEPARAM" which is 58). See ODBC specification or examine your sqlext.h and sql.h
header files for all the SQL_API_XXX macros.

If called with "SQL_API_ALL_FUNCTIONS" (0), then a 100 element array is returned where each element will
contain a '1' if the ODBC function with that SQL_API_XXX index is supported or '' if it is not.

If called with a specific SQL_API_XXX value for a single function it will return true if the ODBC driver
supports that function, otherwise false.

e.g.

my @x = $dbh->func(0,"GetFunctions");
print "SQLDescribeParam is supported\n" if ($x[58]);

print "SQLDescribeParam is supported\n"
if $dbh->func(58, "GetFunctions");

GetStatistics

This private function is now superceded by DBI's statistics_info method.

See the ODBC specification for the SQLStatistics API. You call SQLStatistics like this:

$dbh->func($catalog, $schema, $table, $unique, 'GetStatistics');

Prior to DBD::ODBC 1.16 $unique was not defined as being true/false or SQL_INDEX_UNIQUE/SQL_INDEX_ALL. In
fact, whatever value you provided for $unique was passed through to the ODBC API SQLStatistics call
unchanged. This changed in 1.16, where $unique became a true/false value which is interpreted into
SQL_INDEX_UNIQUE for true and SQL_INDEX_ALL for false.

GetForeignKeys

This private function is now superceded by DBI's foreign_key_info method.

See the ODBC specification for the SQLForeignKeys API. You call SQLForeignKeys like this:

$dbh->func($pcatalog, $pschema, $ptable,
$fcatalog, $fschema, $ftable,
"GetForeignKeys");

GetPrimaryKeys

This private function is now superceded by DBI's primary_key_info method.

See the ODBC specification for the SQLPrimaryKeys API. You call SQLPrimaryKeys like this:

$dbh->func($catalog, $schema, $table, "GetPrimaryKeys");

data_sources

This private function is now superceded by DBI's data_sources method.

You call data_sources like this:

@dsns = $dbh->func("data_sources);

Handled since 0.21.

GetSpecialColumns

See the ODBC specification for the SQLSpecialColumns API. You call SQLSpecialColumns like this:

$dbh->func($identifier, $catalog, $schema, $table, $scope,
$nullable, 'GetSpecialColumns');

Handled as of version 0.28

ColAttributes

This private function is now superceded by DBI's statement attributes NAME, TYPE, PRECISION, SCALE,
NULLABLE etc).

See the ODBC specification for the SQLColAttributes API. You call SQLColAttributes like this:

$sth->func($column, $ftype, "ColAttributes");

SQL_COLUMN_COUNT = 0
SQL_COLUMN_NAME = 1
SQL_COLUMN_TYPE = 2
SQL_COLUMN_LENGTH = 3
SQL_COLUMN_PRECISION = 4
SQL_COLUMN_SCALE = 5
SQL_COLUMN_DISPLAY_SIZE = 6
SQL_COLUMN_NULLABLE = 7
SQL_COLUMN_UNSIGNED = 8
SQL_COLUMN_MONEY = 9
SQL_COLUMN_UPDATABLE = 10
SQL_COLUMN_AUTO_INCREMENT = 11
SQL_COLUMN_CASE_SENSITIVE = 12
SQL_COLUMN_SEARCHABLE = 13
SQL_COLUMN_TYPE_NAME = 14
SQL_COLUMN_TABLE_NAME = 15
SQL_COLUMN_OWNER_NAME = 16
SQL_COLUMN_QUALIFIER_NAME = 17
SQL_COLUMN_LABEL = 18

Note:Oracle's ODBC driver for linux in instant client 11r1 often returns strange values for column name
e.g., '20291'. It is wiser to use DBI's NAME and NAME_xx attributes for portability.

DescribeCol

Removed in DBD::ODBC 1.40_3

Use the DBI's statement attributes NAME, TYPE, PRECISION, SCALE, NULLABLE etc instead.

Additional bind_col attributes
DBD::ODBC supports a few additional attributes which may be passed to the bind_col method in the
attributes.

DiscardString

See DBI's sql_type_cast utility function.

If you bind a column as a specific type (SQL_INTEGER, SQL_DOUBLE and SQL_NUMERIC are the only ones
supported currently) and you add DiscardString to the prepare attributes then if the returned bound data
is capable of being converted to that type the scalar's pv (the string portion of a scalar) is cleared.

NOTE: post DBD::ODBC 1.37, DBD::ODBC binds all SQL_INTEGER columns as SQL_C_LONG and DiscardString is
irrelevant.

This is especially useful if you are using a module which uses a scalar's flags and/or pv to decide if a
scalar is a number. JSON::XS does this and without this flag you have to add 0 to all bound column data
returning numbers to get JSON::XS to encode it is N instead of "N".

NOTE: For DiscardString you need at least DBI 1.611.

StrictlyTyped

See DBI's sql_type_cast utility function.

See "DiscardString" above.

Specifies that when DBI's sql_type_cast function is called on returned data where a bind type is
specified that if the conversion cannot be performed an error will be raised.

This is probably not a lot of use with DBD::ODBC as if you ask for say an SQL_INTEGER and the data is not
able to be converted to an integer the ODBC driver will probably return "Invalid character value for cast
specification (SQL-22018)".

NOTE: For StrictlyTyped you need at least DBI 1.611.

TreatAsLOB

See "odbc_lob_read".

Tracing
DBD::ODBC now supports the parse_trace_flag and parse_trace_flags methods introduced in DBI 1.42 (see DBI
for a full description). As of DBI 1.604, the only trace flag defined which is relevant to DBD::ODBC is
'SQL' which DBD::ODBC supports by outputting the SQL strings (after modification) passed to the prepare
and do methods.

From DBI 1.617 DBI also defines ENC (encoding), CON (connection) TXN (transaction) and DBD (DBD only)
trace flags. DBI's ENC and CON trace flags are synonymous with DBD::ODBC's odbcunicode and odbcconnection
trace flags though I may remove the DBD::ODBC ones in the future. DBI's DBD trace flag allows output of
only DBD::ODBC trace messages without DBI's trace messages.

Currently DBD::ODBC supports two private trace flags. The 'odbcunicode' flag traces some unicode
operations and the odbcconnection traces the connect process.

To enable tracing of particular flags you use:

$h->trace($h->parse_trace_flags('SQL|odbcconnection'));
$h->trace($h->parse_trace_flags('1|odbcunicode'));

In the first case 'SQL' and 'odbcconnection' tracing is enabled on $h. In the second case trace level 1
is set and 'odbcunicode' tracing is enabled.

If you want to enable a DBD::ODBC private trace flag before connecting you need to do something like:

use DBD::ODBC;
DBI->trace(DBD::ODBC->parse_trace_flag('odbcconnection'));

use DBD::ODBC;
DBI->trace(DBD::ODBC->parse_trace_flags('odbcconnection|odbcunicode'));

DBI_TRACE=odbcconnection|odbcunicode perl myscript.pl

From DBI 1.617 you can output only DBD::ODBC trace messages using

DBI_TRACE=DBD perl myscript.pl

DBD::ODBC outputs tracing at levels 3 and above (as levels 1 and 2 are reserved for DBI).

For comprehensive tracing of DBI method calls without all the DBI internals see DBIx::Log4perl.

Deviations from the DBI specification
last_insert_id

DBD::ODBC does not support DBI's last_insert_id. There is no ODBC defined way of obtaining this
information. Generally the mechanism (and it differs vastly between databases and ODBC drivers) it to
issue a select of some form (e.g., select @@identity or select sequence.currval from dual, etc).

There are literally dozens of databases and ODBC drivers supported by DBD::ODBC and I cannot have them
all. If you know how to retrieve the information for last_insert_id and you mail me the ODBC Driver
name/version and database name/version with a small working example I will collect examples and document
them here.

Microsoft Access. Recent versions of MS Access support select @@identity to retrieve the last insert ID.
See http://support.microsoft.com/kb/815629. Information provided by Robert Freimuth.

Comments in SQL

DBI does not say anything in particular about comments in SQL. DBD::ODBC looks for placeholders in the
SQL string and until 1.24_2 it did not recognise comments in SQL strings so could find what it believes
to be a placeholder in a comment e.g.,

select '1' /* placeholder ? in comment */
select -- named placeholder :named in comment
'1'

I cannot be exact about support for ignoring placeholders in literals but it has existed for a long time
in DBD::ODBC. Support for ignoring placeholders in comments was added in 1.24_2. If you find a case where
a named placeholder is not ignored and should be, see "odbc_ignore_named_placeholders" for a workaround
and mail me an example along with your ODBC driver name.

This is not really a deviation from the DBI specification since DBI allows a driver to avoid the overhead
of creating an DBI statement handle for do().

DBD::ODBC implements "do" by calling SQLExecDirect in ODBC and not SQLPrepare followed by SQLExecute so
"do" is not the same as:

$dbh->prepare($sql)->execute()

It does this to avoid a round-trip to the server so it is faster. Normally this is good but some people
fall foul of this with MS SQL Server if they call a procedure which outputs print statements (e.g.,
backup) as the procedure may not complete. See the DBD::ODBC FAQ and in general you are better to use
prepare/execute when calling procedures.

In addition, you should realise that since DBD::ODBC does not create a DBI statement for do calls, if you
set up an error handler the handle passed in when a do fails will be the database handle and not a
statement handle.

Mixed placeholder types

There are 3 conventions for place holders in DBI. These are '?', ':N' and ':name' (where 'N' is a number
and 'name' is an alpha numeric string not beginning with a number). DBD::ODBC supports all these methods
for naming placeholders but you must only use one method throughout a particular SQL string. If you mix
placeholder methods you will get an error like:

Can't mix placeholder styles (1/2)

Using the same placeholder more than once

DBD::ODBC does not support (currently) the use of one named placeholder more than once in the a single
SQL string. i.e.,

insert into foo values (:bar, :p1, :p2, :bar);

is not supported because 'bar' is used more than once but:

insert into foo values(:bar, :p1, :p2)

is ok. If you do the former you will get an error like:

DBD::ODBC does not yet support binding a named parameter more than once

Binding named placeholders

Although the DBI documentation (as of 1.604) does not say how named parameters are bound Tim Bunce has
said that in Oracle they are bound with the leading ':' as part of the name and that has always been the
case. i.e.,

prepare("insert into mytable values (:fred)");
bind_param(":foo", 1);

DBD::ODBC does not support binding named parameters with the ':' introducer. In the above example you
must use:

bind_param("foo", 1);

In discussion on the dbi-dev list is was suggested that the ':' could be made optional and there were no
basic objections but it has not made it's way into the pod yet.

Sticky Parameter Types

The DBI specification post 1.608 says in bind_param:

The data type is 'sticky' in that bind values passed to execute()
are bound with the data type specified by earlier bind_param()
calls, if any. Portable applications should not rely on being able
to change the data type after the first bind_param call.

DBD::ODBC does allow a parameter to be rebound with another data type as ODBC inherently allows this.
Therefore you can do:

# parameter 1 set as a SQL_LONGVARCHAR
$sth->bind_param(1, $data, DBI::SQL_LONGVARCHAR);
# without the bind above the $data parameter would be either a DBD::ODBC
# internal default or whatever the ODBC driver said it was but because
# parameter types are sticky, the type is still SQL_LONGVARCHAR.
$sth->execute($data);
# change the bound type to SQL_VARCHAR
# some DBDs will ignore the type in the following, DBD::ODBC does not
$sth->bind_param(1, $data, DBI::SQL_VARCHAR);

disconnect and transactions

DBI does not define whether a driver commits or rolls back any outstanding transaction when disconnect is
called. As such DBD::ODBC cannot deviate from the specification but you should know it rolls back an
uncommitted transaction when disconnect is called if SQLDisconnect returns state 25000 (transaction in
progress).

execute_for_fetch and execute_array

From version 1.34_1 DBD::ODBC implements its own execute_for_fetch which binds arrays of parameters and
can send multiple rows ("odbc_batch_size") of parameters through the ODBC driver in one go (this
overrides DBI's default execute_for_fetch). This is much faster when inserting, updating or deleting many
rows in one go. Note, execute_array uses execute_for_fetch when the parameters are passed for column-wise
binding.

NOTE: DBD::ODBC 1.34_1 to DBD::ODBC 1.36_1 set the default to use DBD::ODBC's own execute_for_fetch but
quite a few ODBC drivers just cannot handle it. As such, from DBD::ODBC 1.36_2 the default was changed to
not use DBD::ODBC's execute_for_fetch (i.e., you need to enable it with odbc_array_operations).

NOTE: Some ODBC drivers don't support setting SQL_ATTR_PARAMSET_SIZE > 1, and hence cannot support
binding arrays of parameters. The only way to detect this is to attempt to set SQL_ATTR_PARAMSET_SIZE to
a value greater than 1 and it is too late once someone has called execute_for_fetch. I don't want to add
test code on each connect to test for this as it will affect everyone, even those not using the native
execute_for_fetch so for now it is a suck it and see. For your information MS Access which does not
support arrays of parameters errors with HY092, "Invalid attribute/option identifier".

However, there are a small number of differences between using DBD::ODBC's execute_for_fetch compared
with using DBI's default implementation (which simply calls execute repeatedly once per row). The
differences you may see are:

o as DBI's execute_for_fetch does one row at a time the result from execute is for one row and just about
all ODBC drivers can report the number of affected rows when SQLRowCount is called per execute. When
batches of parameters are sent the driver can still return the number of affected rows but it is usually
per batch rather than per row. As a result, the tuple_status array you may pass to execute_for_fetch (or
execute_array) usually shows -1 (unknown) for each row although the total affected returned in array
context is a correct total affected.

o not all ODBC drivers have sufficient ODBC support (arguably a bug) for correct diagnostics support when
using arrays. DBI dictates that if a row in the batch is in error the tuple_status will contain the
state, native and error message text. However the batch may generate multiple errors per row (which DBI
says nothing about) and more than one row may error. In ODBC we get a list of errors but to associate
each one with a particular row we need to call SQLGetDiagField for SQL_DIAG_ROW_NUMBER and it should say
which row in the batch the diagnostic is associated with. Some ODBC drivers do not support
SQL_DIAG_ROW_NUMBER properly and then DBD::ODBC cannot know which row in the batch an error refers to. In
this case DBD::ODBC will report an error saying "failed to retrieve diags", state of HY000 and a native
of 1 so you'll still see an error but not necessarily the exact one. Also, when more than one diagnostic
is found for a row DBD::ODBC picks the first one (which is usually most relevant) as there is no way to
report more than one diagnostic per row in the tuple_status. If the first problem of SQL_DIAG_ROW_NUMBER
proves to be a problem for you the DBD::ODBC tracing will show all errors and you can also use
"odbc_getdiagrec" yourself.

o Binding parameters with execute_array and execute_for_fetch does not allow the parameter types to be
set. However, as parameter types are sticky you can call bind_param(param_num, undef, {TYPE => sql_type})
before calling execute_for_fetch/execute_array and the TYPE should be sticky when the batch of parameters
is bound.

o Although you can insert very large columns execute_for_fetch will need "odbc_batch_size" * max length
of parameter per parameter so you may hit memory limits. If you use DBI's execute_for_fetch DBD::ODBC
uses the ODBC API SQLPutData (see "odbc_putdata_start") which does not require large amounts of memory as
large columns are sent in pieces.

o A lot of drivers have bugs with arrays of parameters (see the ODBC FAQ). e.g., as of 18-MAR-2012 I've
seen the latest SQLite ODBC driver seg fault and freeTDS 8/0.91 returns the wrong row count for batches.

o DO NOT attempt to do an insert/update/delete and a select in the same SQL with execute_array e.g.,

SET IDENTITY_INSERT mytable ON
insert into mytable (id, name) values (?,?)
SET IDENTITY_INSERT mytable OFF
SELECT SCOPE_IDENTITY()

It just won't/can't work although you may not have noticed when using DBI's inbuilt execute_* methods.
See rt 75687.

type_info_all

Many ODBC drivers now return 20 columns in type_info_all rather than the 19 DBI documents. The 20th
column is usually called "USERTYPE". Recent MS SQL Server ODBC drivers do this. Fortunately this should
not adversely affect you so long as you are using the keys provided at the start of type_info_all.

Binding Columns

The DBI specification allows a column type to be overridden in the call to the bind_col method. Mostly,
DBD::ODBC ignores this type as it binds integers (SQL_INTEGER) as a SQL_C_LONG (since DBD::ODBC 1.38_1)
and all other columns as SQL_C_CHAR or SQL_C_WCHAR and it is too late to change the bind type after the
result-set has been described anyway. The only time when the TYPE passed to bind_col is used in DBD::ODBC
is when it is SQL_NUMERIC or SQL_DOUBLE in which case DBD::ODBC will call DBI's sql_type_cast method.

Since DBD::ODBC 1.38_1 if you attempt to change the bind type after the column has already bound
DBD::ODBC will issue a warning and ignore your column type change e.g.,

my $s = $h->prepare(q/select a from mytable);
$s->execute; # The column type was determined here
my $r;
$s->bind_col(1, \$r); # and bound as the right type here
$s->execute;
$s->bind_col(1, \$r, {TYPE => SQL_XXX}); # warning, type changed

Basically, if you are passing a TYPE to bind_col with DBD::ODBC (other than SQL_NUMERIC or SQL_DOUBLE)
your code is probably wrong.

Significant changes occurred in DBD::ODBC at 1.38_1 for binding columns. Please see the Changes file.

Unicode
The ODBC specification supports wide character versions (a postfix of 'W') of some of the normal ODBC
APIs e.g., SQLDriverConnectW is a wide character version of SQLDriverConnect.

In ODBC on Windows the wide characters are defined as SQLWCHARs (2 bytes) and are UCS-2 (but UTF-16 is
accepted by some drivers now e.g., MS SQL Server 2012 and the new collation suffix _SC which stands for
Supplementary Character Support). On non-Windows, the main driver managers I know of have implemented the
wide character APIs differently:

unixODBC
unixODBC mimics the Windows ODBC API precisely meaning the wide character versions expect and return
2-byte characters in UCS-2 or UTF-16.

unixODBC will happily recognise ODBC drivers which only have the ANSI versions of the ODBC API and
those that have the wide versions too.

unixODBC will allow an ANSI application to work with a unicode ODBC driver and vice versa (although
in the latter case you obviously cannot actually use unicode).

unixODBC does not prevent you sending UTF-8 in the ANSI versions of the ODBC APIs but whether that is
understood by your ODBC driver is another matter.

unixODBC differs in only one way from the Microsoft ODBC driver in terms of unicode support in that
it avoids unnecessary translations between single byte and double byte characters when an ANSI
application is using a unicode-aware ODBC driver by requiring unicode applications to signal their
intent by calling SQLDriverConnectW first. On Windows, the ODBC driver manager always uses the wide
versions of the ODBC API in ODBC drivers which provide the wide versions regardless of what the
application really needs and this results in a lot of unnecessary character translations when you
have an ANSI application and a unicode ODBC driver.

iODBC
The wide character versions expect and return wchar_t types.

DBD::ODBC has gone with unixODBC so you cannot use iODBC with a unicode build of DBD::ODBC. However, some
ODBC drivers support UTF-8 (although how they do this with SQLGetData reliably I don't know) and so you
should be able to use those with DBD::ODBC not built for unicode.

Enabling and Disabling Unicode support

On Windows Unicode support is enabled by default and to disable it you will need to specify "-nou" to
Makefile.PL to get back to the original behavior of DBD::ODBC before any Unicode support was added.

e.g.,

perl Makfile.PL -nou

On non-Windows platforms Unicode support is disabled by default. To enable it specify "-u" to Makefile.PL
when you configure DBD::ODBC.

e.g.,

perl Makefile.PL -u

Unicode - What is supported?

As of version 1.17 DBD::ODBC has the following unicode support:

SQL (introduced in 1.16_2)
Unicode strings in calls to the "prepare" and "do" methods are supported so long as the
"odbc_execdirect" attribute is not used.

unicode connection strings (introduced in 1.16_2)
Unicode connection strings are supported but you will need a DBI post 1.607 for that.

column names
Unicode column names are returned.

bound columns (introduced in 1.15)
If the DBMS reports the column as being a wide character (SQL_Wxxx) it will be bound as a wide
character and any returned data will be converted from UTF-16 to UTF-8 and the UTF-8 flag will then
be set on the data.

bound parameters
If the perl scalars you bind to parameters are marked UTF-8 and the DBMS reports the type as being a
wide type or you bind the parameter as a wide type they will be converted to wide characters and
bound as such.

metadata calls like table_info, column_info
As of DBD::ODBC 1.32_3 meta data calls accept Unicode strings.

Since version 1.16_4, the default parameter bind type is SQL_WVARCHAR for unicode builds of DBD::ODBC.
This only affects ODBC drivers which do not support SQLDescribeParam and only then if you do not
specifically set a SQL type on the bind_param method call.

The above Unicode support has been tested with the SQL Server, Oracle 9.2+ and Postgres drivers on
Windows and various Easysoft ODBC drivers on UNIX.

Unicode - What is not supported?

You cannot use unicode parameter names e.g.,

select * from table where column = :unicode_param_name

You cannot use unicode strings in calls to prepare if you set the odbc_execdirect attribute.

You cannot use the iODBC driver manager with DBD::ODBC built for unicode.

Unicode - Caveats

For Unicode support on any platform in Perl you will need at least Perl 5.8.1 - sorry but this is the way
it is with Perl.

The Unicode support in DBD::ODBC expects a WCHAR to be 2 bytes (as it is on Windows and as the ODBC
specification suggests it is). Until ODBC specifies any other Unicode support it is not envisioned this
will change. On UNIX there are a few different ODBC driver managers. I have only tested the unixODBC
driver manager (http://www.unixodbc.org) with Unicode support and it was built with defaults which set
WCHAR as 2 bytes.

I believe that the iODBC driver manager expects wide characters to be wchar_t types (which are usually 4)
and hence DBD::ODBC will not work iODBC when built for unicode.

The ODBC Driver must expect Unicode data specified in SQLBindParameter and SQLBindCol to be UTF-16 in
local endianness. Similarly, in calls to SQLPrepareW, SQLDescribeColW and SQLDriverConnectW.

You should be aware that once Unicode support is enabled it affects a number of DBI methods (some of
which you might not expect). For instance, when listing tables, columns etc some drivers (e.g. Microsoft
SQL Server) will report the column types as wide types even if the strings actually fit in 7-bit ASCII.
As a result, there is an overhead for retrieving this column data as 2 bytes per character will be
transmitted (compared with 1 when Unicode support is not enabled) and these strings will be converted
into UTF-8 but will end up fitting (in most cases) into 7bit ASCII so a lot of conversion work has been
performed for nothing. If you don't have Unicode table and column names or Unicode column data in your
tables you are best disabling Unicode support.

I am at present unsure if ChopBlanks processing on Unicode strings is working correctly on UNIX. If
nothing else the construct L' ' in dbdimp.c might not work with all UNIX compilers. Reports of issues and
patches welcome.

Unicode implementation in DBD::ODBC

DBD::ODBC uses the wide character versions of the ODBC API and the SQL_WCHAR ODBC type to support unicode
in Perl.

Wide characters returned from the ODBC driver will be converted to UTF-8 and the perl scalars will have
the utf8 flag set (by using sv_utf8_decode).

IMPORTANT

Perl scalars which are UTF-8 and are sent through the ODBC API will be converted to UTF-16 and passed to
the ODBC wide APIs or signalled as SQL_WCHARs (e.g., in the case of bound columns). Retrieved data which
are wide characters are converted from UTF-16 to UTF-8. However, you should realise most ODBC drivers do
not support UTF-16, ODBC only talks about wide characters being 2 bytes and UCS-2 and UCS-2 and UTF-16
are not the same. UCS-2 only supports Unicode characters in the first plane (the Basic Multilangual Plane
or BMP) (code points U+0000 to U+FFFF), the most frequently used characters. So why does DBD::ODBC
currently encode in UTF-16? For around 97% of Unicode characters in the range 0-0xFFFF UCS-2 and UTF-16
are exactly the same (and where they differ there is no valid Unicode character as the range U+D800 to
U+DFFF is reserved from use only as surrogate pairs). As the ODBC API currently uses UCS-2 it does not
support Unicode characters with code points above 0xFFFF (if you know better I'd like to hear from you).
However, because DBD::ODBC uses UTF-16 encoding you can still insert Unicode characters above 0xFFFF into
your database and retrieve them back correctly but they may not being treated as a single Unicode
character in your database e.g., a "select length(a_column) from table" with a single Unicode character
above 0xFFFF may return 2 and not 1 so you cannot use database functions on that data like
upper/lower/length etc but you can at least save the data in your database and get it back.

When built for unicode, DBD::ODBC will always call SQLDriverConnectW (and not SQLDriverConnect) even if
a) your connection string is not unicode b) you have not got a DBI later than 1.607, because unixODBC
requires SQLDriverConnectW to be called if you want to call other unicode ODBC APIs later. As a result,
if you build for unicode and pass ASCII strings to the connect method they will be converted to UTF-16
and passed to SQLDriverConnectW. This should make no real difference to perl not using unicode connection
strings.

You will need a DBI later than 1.607 to support unicode connection strings because until post 1.607 there
was no way for DBI to pass unicode strings to the DBD.

Unicode and Oracle

You have to set the environment variables "NLS_NCHAR=AL32UTF8" and "NLS_LANG=AMERICAN_AMERICA.AL32UTF8"
(or any other language setting ending with ".AL32UTF8") before loading DBD::ODBC to make Oracle return
Unicode data. (See also "Oracle and Unicode" in the POD of DBD::Oracle.)

On Windows, using the Oracle ODBC Driver you have to enable the Force SQL_WCHAR support Workaround in the
data source configuration to make Oracle return Unicode to a non-Unicode application. Alternatively, you
can include "FWC=T" in your connect string.

Unless you need to use ODBC, if you want Unicode support with Oracle you are better off using
DBD::Oracle.

Unicode and PostgreSQL

See the odbc_utf8_on parameter to treat all strings as utf8.

Some tests from the original DBD::ODBC 1.13 fail with PostgreSQL 8.0.3, so you may not want to use
DBD::ODBC to connect to PostgreSQL 8.0.3.

Unicode tests fail because PostgreSQL seems not to give any hints about Unicode, so all data is treated
as non-Unicode.

Unless you need to use ODBC, if you want Unicode support with Postgres you are better off with DBD::Pg as
it has a specific attribute named "pg_enable_utf8" to enable Unicode support.

Unicode and Easysoft ODBC Drivers

We have tested the Easysoft SQL Server, Oracle and ODBC Bridge drivers with DBD::ODBC built for Unicode.
All work as described without modification except for the Oracle driver you will need to set you NLS_LANG
as mentioned above.

Unicode and other ODBC drivers

If you have a unicode-enabled ODBC driver and it works with DBD::ODBC let me know and I will include it
here.

ODBC Support in ODBC Drivers
Drivers without SQLDescribeParam

Some drivers do not support the "SQLDescribeParam" ODBC API (e.g., Microsoft Access, FreeTDS).

DBD::ODBC uses the "SQLDescribeParam" API when parameters are bound to your SQL to find the types of the
parameters. If the ODBC driver does not support "SQLDescribeParam", DBD::ODBC assumes the parameters are
"SQL_VARCHAR" or "SQL_WVARCHAR" types (depending on whether DBD::ODBC is built for unicode or not). In
any case, if you bind a parameter and specify a SQL type this overrides any type DBD::ODBC would choose.

For ODBC drivers which do not support "SQLDescribeParam" the default behavior in DBD::ODBC may not be
what you want. To change the default parameter bind type set "odbc_default_bind_type". If, after that you
have some SQL where you need to vary the parameter types used add the SQL type to the end of the
"bind_param" method.

use DBI qw(:sql_types);
$h = DBI->connect;
# set the default bound parameter type
$h->{odbc_default_bind_type} = SQL_VARCHAR;
# bind a parameter with a specific type
$s = $h->prepare(q/insert into mytable values(?)/);
$s->bind_param(1, "\x{263a}", SQL_WVARCHAR);

Version Control
DBD::ODBC source code was under version control at svn.perl.org until April 2013 when svn.perl.org was
closed down and it is now on github at https://github.com/perl5-dbi/DBD-ODBC.git.

Contributing
There are a number of ways you may help with the development and maintenance of this module:

Submitting patches
Please send me a git pull request or email a unified diff.

Please try and include a test which demonstrates the fix/change working.

Reporting installs
Install CPAN::Reporter and report you installations. This is easy to do - see "CPAN Testers
Reporting".

Report bugs
If you find what you believe is a bug then enter it into the
<http://rt.cpan.org/Dist/Display.html?Name=DBD-ODBC> system. Where possible include code which
reproduces the problem including any schema required and the versions of software you are using.

If you are unsure whether you have found a bug report it anyway or post it to the dbi-users mailing
list.

pod comments and corrections
If you find inaccuracies in the DBD::ODBC pod or have a comment which you think should be added then
go to <http://annocpan.org> and submit them there. I get an email for every comment added and will
review each one and apply any changes to the documentation.

Review DBD::ODBC
Add your review of DBD::ODBC on <http://cpanratings.perl.org>.

If you are a member on ohloh then add your review or register your use of DBD::ODBC at
<http://www.ohloh.net/projects/perl_dbd_odbc>.

submit test cases
Most DBDs are built against a single client library for the database.

Unlike other DBDs, DBD::ODBC works with many different ODBC drivers. Although they all should be
written with regard to the ODBC specification drivers have bugs and in some places the specification
is open to interpretation. As a result, when changes are applied to DBD::ODBC it is very easy to
break something in one ODBC driver.

What helps enormously to identify problems in the many combinations of DBD::ODBC and ODBC drivers is
a large test suite. I would greatly appreciate any test cases and in particular any new test cases
for databases other than MS SQL Server.

Test DBD::ODBC
I have a lot of problems deciding when to move a development release to an official release since I
get few test reports for development releases. What often happens is I call for testers on various
lists, get a few and then get inundated with requests to do an official release. Then I do an
official release and loads of rts appear out of nowhere and the cycle starts again.

DBD::ODBC by its very nature works with many ODBC Drivers and it is impossible for me to have and
test them all (this differs from other DBDs). If you depend on DBD::ODBC you should be interested in
new releases and if you send me your email address suggesting you are prepared to be part of the
DBD::ODBC testing network I will credit you in the Changes file and perhaps the main DBD::ODBC file.

CPAN Testers Reporting
Please, please, please (is that enough), consider installing CPAN::Reporter so that when you install perl
modules a report of the installation success or failure can be sent to cpan testers. In this way module
authors 1) get feedback on the fact that a module is being installed 2) get to know if there are any
installation problems. Also other people like you may look at the test reports to see how successful they
are before choosing the version of a module to install.

See this guide on how to get started with sending test reports:
<http://wiki.cpantesters.org/wiki/QuickStart>.

Others/todo?
Level 2

SQLColumnPrivileges
SQLProcedureColumns
SQLProcedures
SQLTablePrivileges
SQLDrivers
SQLNativeSql

Random Links
These are in need of sorting and annotating. Some are relevant only to ODBC developers.

You can find DBD::ODBC on ohloh now at:

<http://www.ohloh.net/projects/perl_dbd_odbc>

If you use ohloh and DBD::ODBC please say you use it and rate it.

There is a good search engine for the various Perl DBI lists at the following URLS:

<http://perl.markmail.org/search/list:org.perl.dbi-users>

<http://perl.markmail.org/search/list:org.perl.dbi-dev>

<http://perl.markmail.org/search/list:org.perl.dbi-announce>

<http://www.syware.com>

<http://www.microsoft.com/odbc>

For Linux/Unix folks, compatible ODBC driver managers can be found at:

<http://www.unixodbc.org> (unixODBC source and rpms)

<http://www.iodbc.org> (iODBC driver manager source)

For Linux/Unix folks, you can checkout the following for ODBC Drivers and Bridges:

<http://www.easysoft.com>

<http://www.openlinksw.com>

<http://www.datadirect.com>

<http://www.atinet.com>

Some useful tutorials:
Debugging Perl DBI:

<http://www.easysoft.com/developer/languages/perl/dbi-debugging.html>

Enabling ODBC support in Perl with Perl DBI and DBD::ODBC:

<http://www.easysoft.com/developer/languages/perl/dbi_dbd_odbc.html>

Perl DBI/DBD::ODBC Tutorial Part 1 - Drivers, Data Sources and Connection:

<http://www.easysoft.com/developer/languages/perl/dbd_odbc_tutorial_part_1.html>

Perl DBI/DBD::ODBC Tutorial Part 2 - Introduction to retrieving data from your database:

<http://www.easysoft.com/developer/languages/perl/dbd_odbc_tutorial_part_2.html>

Perl DBI/DBD::ODBC Tutorial Part 3 - Connecting Perl on UNIX or Linux to Microsoft SQL Server:

<http://www.easysoft.com/developer/languages/perl/sql_server_unix_tutorial.html>

Perl DBI - Put Your Data On The Web:

<http://www.easysoft.com/developer/languages/perl/tutorial_data_web.html>

Multiple Active Statements (MAS) and DBD::ODBC

<http://www.easysoft.com/developer/languages/perl/multiple-active-statements.html>

64-bit ODBC

<http://www.easysoft.com/developer/interfaces/odbc/64-bit.html>

How do I insert Unicode supplementary characters into SQL Server from Perl?

<http://www.easysoft.com/support/kb/kb01043.html>

Frequently Asked Questions
Frequently asked questions are now in DBD::ODBC::FAQ. Run "perldoc DBD::ODBC::FAQ" to view them.

CONFIGURATION AND ENVIRONMENT

       You should consult the documentation for the ODBC Driver Manager you are using.

DEPENDENCIES

       DBI

       Test::Simple

INCOMPATIBILITIES

       None known.

BUGS AND LIMITATIONS

       None  known  other than the deviations from the DBI specification mentioned above in "Deviations from the
       DBI specification".

       Please report any to me via the CPAN RT system. See <http://rt.cpan.org/> for more details.

AUTHOR

       Tim Bunce

       Jeff Urlwin

       Thomas K. Wenrich

       Martin J. Evans

LICENSE AND COPYRIGHT

       This program is free software; you can redistribute it and/or modify it under  the  same  terms  as  Perl
       itself. See perlartistic. This program is distributed in the hope that it will be useful, but WITHOUT ANY
       WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

       Portions  of  this software are Copyright Tim Bunce, Thomas K. Wenrich, Jeff Urlwin and Martin J. Evans -
       see the source.