Provided by: libdbd-sqlite3-perl_1.56-1_amd64 
NAME
DBD::SQLite - Self-contained RDBMS in a DBI Driver
SYNOPSIS
use DBI;
my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");
DESCRIPTION
SQLite is a public domain file-based relational database engine that you can find at
<http://www.sqlite.org/>.
DBD::SQLite is a Perl DBI driver for SQLite, that includes the entire thing in the distribution. So in
order to get a fast transaction capable RDBMS working for your perl project you simply have to install
this module, and nothing else.
SQLite supports the following features:
Implements a large subset of SQL92
See <http://www.sqlite.org/lang.html> for details.
A complete DB in a single disk file
Everything for your database is stored in a single disk file, making it easier to move things around
than with DBD::CSV.
Atomic commit and rollback
Yes, DBD::SQLite is small and light, but it supports full transactions!
Extensible
User-defined aggregate or regular functions can be registered with the SQL parser.
There's lots more to it, so please refer to the docs on the SQLite web page, listed above, for SQL
details. Also refer to DBI for details on how to use DBI itself. The API works like every DBI module
does. However, currently many statement attributes are not implemented or are limited by the typeless
nature of the SQLite database.
SQLITE VERSION
DBD::SQLite is usually compiled with a bundled SQLite library (SQLite version 3.22.0 as of this release)
for consistency. However, a different version of SQLite may sometimes be used for some reasons like
security, or some new experimental features.
You can look at $DBD::SQLite::sqlite_version ("3.x.y" format) or $DBD::SQLite::sqlite_version_number
("3xxxyyy" format) to find which version of SQLite is actually used. You can also check
"DBD::SQLite::Constants::SQLITE_VERSION_NUMBER()".
You can also find how the library is compiled by calling "DBD::SQLite::compile_options()" (see below).
NOTABLE DIFFERENCES FROM OTHER DRIVERS
Database Name Is A File Name
SQLite creates a file per a database. You should pass the "path" of the database file (with or without a
parent directory) in the DBI connection string (as a database "name"):
my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");
The file is opened in read/write mode, and will be created if it does not exist yet.
Although the database is stored in a single file, the directory containing the database file must be
writable by SQLite because the library will create several temporary files there.
If the filename $dbfile is ":memory:", then a private, temporary in-memory database is created for the
connection. This in-memory database will vanish when the database connection is closed. It is handy for
your library tests.
Note that future versions of SQLite might make use of additional special filenames that begin with the
":" character. It is recommended that when a database filename actually does begin with a ":" character
you should prefix the filename with a pathname such as "./" to avoid ambiguity.
If the filename $dbfile is an empty string, then a private, temporary on-disk database will be created.
This private database will be automatically deleted as soon as the database connection is closed.
As of 1.41_01, you can pass URI filename (see <http://www.sqlite.org/uri.html>) as well for finer
control:
my $dbh = DBI->connect("dbi:SQLite:uri=file:$path_to_dbfile?mode=rwc");
Note that this is not for remote SQLite database connection. You can only connect to a local database.
Read-Only Database
You can set sqlite_open_flags (only) when you connect to a database:
use DBD::SQLite::Constants qw/:file_open/;
my $dbh = DBI->connect("dbi:SQLite:$dbfile", undef, undef, {
sqlite_open_flags => SQLITE_OPEN_READONLY,
});
See <http://www.sqlite.org/c3ref/open.html> for details.
As of 1.49_05, you can also make a database read-only by setting "ReadOnly" attribute to true (only) when
you connect to a database. Actually you can set it after you connect, but in that case, it can't make
the database read-only, and you'll see a warning (which you can hide by turning "PrintWarn" off).
DBD::SQLite And File::Temp
When you use File::Temp to create a temporary file/directory for SQLite databases, you need to remember:
tempfile may be locked exclusively
You may want to use "tempfile()" to create a temporary database filename for DBD::SQLite, but as
noted in File::Temp's POD, this file may have an exclusive lock under some operating systems (notably
Mac OSX), and result in a "database is locked" error. To avoid this, set EXLOCK option to false when
you call tempfile().
($fh, $filename) = tempfile($template, EXLOCK => 0);
CLEANUP may not work unless a database is disconnected
When you set CLEANUP option to true when you create a temporary directory with "tempdir()" or
"newdir()", you may have to disconnect databases explicitly before the temporary directory is gone
(notably under MS Windows).
(The above is quoted from the pod of File::Temp.)
If you don't need to keep or share a temporary database, use ":memory:" database instead. It's much
handier and cleaner for ordinary testing.
DBD::SQLite and fork()
Follow the advice in the SQLite FAQ (<https://sqlite.org/faq.html>).
Under Unix, you should not carry an open SQLite database across a fork() system call into the child
process. Problems will result if you do.
You shouldn't (re)use a database handle you created (probably to set up a database schema etc) before you
fork(). Otherwise, you might see a database corruption in the worst case.
If you need to fork(), (re)open a database after you fork(). You might also want to tweak
"sqlite_busy_timeout" and "sqlite_use_immediate_transaction" (see below), depending on your needs.
If you need a higher level of concurrency than SQLite supports, consider using other client/server
database engines.
Accessing A Database With Other Tools
To access the database from the command line, try using "dbish" which comes with the DBI::Shell module.
Just type:
dbish dbi:SQLite:foo.db
On the command line to access the file foo.db.
Alternatively you can install SQLite from the link above without conflicting with DBD::SQLite and use the
supplied "sqlite3" command line tool.
Blobs
As of version 1.11, blobs should "just work" in SQLite as text columns. However this will cause the data
to be treated as a string, so SQL statements such as length(x) will return the length of the column as a
NUL terminated string, rather than the size of the blob in bytes. In order to store natively as a BLOB
use the following code:
use DBI qw(:sql_types);
my $dbh = DBI->connect("dbi:SQLite:dbfile","","");
my $blob = `cat foo.jpg`;
my $sth = $dbh->prepare("INSERT INTO mytable VALUES (1, ?)");
$sth->bind_param(1, $blob, SQL_BLOB);
$sth->execute();
And then retrieval just works:
$sth = $dbh->prepare("SELECT * FROM mytable WHERE id = 1");
$sth->execute();
my $row = $sth->fetch;
my $blobo = $row->[1];
# now $blobo == $blob
Functions And Bind Parameters
As of this writing, a SQL that compares a return value of a function with a numeric bind value like this
doesn't work as you might expect.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->execute(5);
This is because DBD::SQLite assumes that all the bind values are text (and should be quoted) by default.
Thus the above statement becomes like this while executing:
SELECT bar FROM foo GROUP BY bar HAVING count(*) > "5";
There are three workarounds for this.
Use bind_param() explicitly
As shown above in the "BLOB" section, you can always use "bind_param()" to tell the type of a bind
value.
use DBI qw(:sql_types); # Don't forget this
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->bind_param(1, 5, SQL_INTEGER);
$sth->execute();
Add zero to make it a number
This is somewhat weird, but works anyway.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > (? + 0);
});
$sth->execute(5);
Set "sqlite_see_if_its_a_number" database handle attribute
As of version 1.32_02, you can use "sqlite_see_if_its_a_number" to let DBD::SQLite to see if the bind
values are numbers or not.
$dbh->{sqlite_see_if_its_a_number} = 1;
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->execute(5);
You can set it to true when you connect to a database.
my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
AutoCommit => 1,
RaiseError => 1,
sqlite_see_if_its_a_number => 1,
});
This is the most straightforward solution, but as noted above, existing data in your databases
created by DBD::SQLite have not always been stored as numbers, so this *might* cause other obscure
problems. Use this sparingly when you handle existing databases. If you handle databases created by
other tools like native "sqlite3" command line tool, this attribute would help you.
As of 1.41_04, "sqlite_see_if_its_a_number" works only for bind values with no explicit type.
my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
AutoCommit => 1,
RaiseError => 1,
sqlite_see_if_its_a_number => 1,
});
my $sth = $dbh->prepare('INSERT INTO foo VALUES(?)');
# '1.230' will be inserted as a text, instead of 1.23 as a number,
# even though sqlite_see_if_its_a_number is set.
$sth->bind_param(1, '1.230', SQL_VARCHAR);
$sth->execute;
Placeholders
SQLite supports several placeholder expressions, including "?" and ":AAAA". Consult the DBI and SQLite
documentation for details.
<http://www.sqlite.org/lang_expr.html#varparam>
Note that a question mark actually means a next unused (numbered) placeholder. You're advised not to use
it with other (numbered or named) placeholders to avoid confusion.
my $sth = $dbh->prepare(
'update TABLE set a=?1 where b=?2 and a IS NOT ?1'
);
$sth->execute(1, 2);
Pragma
SQLite has a set of "Pragma"s to modify its operation or to query for its internal data. These are
specific to SQLite and are not likely to work with other DBD libraries, but you may find some of these
are quite useful, including:
journal_mode
You can use this pragma to change the journal mode for SQLite databases, maybe for better
performance, or for compatibility.
Its default mode is "DELETE", which means SQLite uses a rollback journal to implement transactions,
and the journal is deleted at the conclusion of each transaction. If you use "TRUNCATE" instead of
"DELETE", the journal will be truncated, which is usually much faster.
A "WAL" (write-ahead log) mode is introduced as of SQLite 3.7.0. This mode is persistent, and it
stays in effect even after closing and reopening the database. In other words, once the "WAL" mode is
set in an application or in a test script, the database becomes inaccessible by older clients. This
tends to be an issue when you use a system "sqlite3" executable under a conservative operating
system.
To fix this, You need to issue "PRAGMA journal_mode = DELETE" (or "TRUNCATE") beforehand, or install
a newer version of "sqlite3".
legacy_file_format
If you happen to need to create a SQLite database that will also be accessed by a very old SQLite
client (prior to 3.3.0 released in Jan. 2006), you need to set this pragma to ON before you create a
database.
reverse_unordered_selects
You can set this pragma to ON to reverse the order of results of SELECT statements without an ORDER
BY clause so that you can see if applications are making invalid assumptions about the result order.
Note that SQLite 3.7.15 (bundled with DBD::SQLite 1.38_02) enhanced its query optimizer and the order
of results of a SELECT statement without an ORDER BY clause may be different from the one of the
previous versions.
synchronous
You can set set this pragma to OFF to make some of the operations in SQLite faster with a possible
risk of database corruption in the worst case. See also "Performance" section below.
See <http://www.sqlite.org/pragma.html> for more details.
Foreign Keys
SQLite has started supporting foreign key constraints since 3.6.19 (released on Oct 14, 2009; bundled in
DBD::SQLite 1.26_05). To be exact, SQLite has long been able to parse a schema with foreign keys, but
the constraints has not been enforced. Now you can issue a "foreign_keys" pragma to enable this feature
and enforce the constraints, preferably as soon as you connect to a database and you're not in a
transaction:
$dbh->do("PRAGMA foreign_keys = ON");
And you can explicitly disable the feature whenever you like by turning the pragma off:
$dbh->do("PRAGMA foreign_keys = OFF");
As of this writing, this feature is disabled by default by the SQLite team, and by us, to secure backward
compatibility, as this feature may break your applications, and actually broke some for us. If you have
used a schema with foreign key constraints but haven't cared them much and supposed they're always
ignored for SQLite, be prepared, and please do extensive testing to ensure that your applications will
continue to work when the foreign keys support is enabled by default.
See <http://www.sqlite.org/foreignkeys.html> for details.
Transactions
DBI/DBD::SQLite's transactions may be a bit confusing. They behave differently according to the status of
the "AutoCommit" flag:
When the AutoCommit flag is on
You're supposed to always use the auto-commit mode, except you explicitly begin a transaction, and
when the transaction ended, you're supposed to go back to the auto-commit mode. To begin a
transaction, call "begin_work" method, or issue a "BEGIN" statement. To end it, call
"commit/rollback" methods, or issue the corresponding statements.
$dbh->{AutoCommit} = 1;
$dbh->begin_work; # or $dbh->do('BEGIN TRANSACTION');
# $dbh->{AutoCommit} is turned off temporarily during a transaction;
$dbh->commit; # or $dbh->do('COMMIT');
# $dbh->{AutoCommit} is turned on again;
When the AutoCommit flag is off
You're supposed to always use the transactional mode, until you explicitly turn on the AutoCommit
flag. You can explicitly issue a "BEGIN" statement (only when an actual transaction has not begun
yet) but you're not allowed to call "begin_work" method (if you don't issue a "BEGIN", it will be
issued internally). You can commit or roll it back freely. Another transaction will automatically
begin if you execute another statement.
$dbh->{AutoCommit} = 0;
# $dbh->do('BEGIN TRANSACTION') is not necessary, but possible
...
$dbh->commit; # or $dbh->do('COMMIT');
# $dbh->{AutoCommit} stays intact;
$dbh->{AutoCommit} = 1; # ends the transactional mode
This "AutoCommit" mode is independent from the autocommit mode of the internal SQLite library, which
always begins by a "BEGIN" statement, and ends by a "COMMIT" or a <ROLLBACK>.
Transaction and Database Locking
The default transaction behavior of SQLite is "deferred", that means, locks are not acquired until the
first read or write operation, and thus it is possible that another thread or process could create a
separate transaction and write to the database after the "BEGIN" on the current thread has executed, and
eventually cause a "deadlock". To avoid this, DBD::SQLite internally issues a "BEGIN IMMEDIATE" if you
begin a transaction by calling "begin_work" or by turning off "AutoCommit" (since 1.38_01).
If you really need to turn off this feature for some reasons, set "sqlite_use_immediate_transaction"
database handle attribute to false, and the default "deferred" transaction will be used.
my $dbh = DBI->connect("dbi:SQLite::memory:", "", "", {
sqlite_use_immediate_transaction => 0,
});
Or, issue a "BEGIN" statement explicitly each time you begin a transaction.
See <http://sqlite.org/lockingv3.html> for locking details.
"$sth->finish" and Transaction Rollback
As the DBI doc says, you almost certainly do not need to call "finish" in DBI method if you fetch all
rows (probably in a loop). However, there are several exceptions to this rule, and rolling-back of an
unfinished "SELECT" statement is one of such exceptional cases.
SQLite prohibits "ROLLBACK" of unfinished "SELECT" statements in a transaction (See
<http://sqlite.org/lang_transaction.html> for details). So you need to call "finish" before you issue a
rollback.
$sth = $dbh->prepare("SELECT * FROM t");
$dbh->begin_work;
eval {
$sth->execute;
$row = $sth->fetch;
...
die "For some reason";
...
};
if($@) {
$sth->finish; # You need this for SQLite
$dbh->rollback;
} else {
$dbh->commit;
}
Processing Multiple Statements At A Time
DBI's statement handle is not supposed to process multiple statements at a time. So if you pass a string
that contains multiple statements (a "dump") to a statement handle (via "prepare" or "do"), DBD::SQLite
only processes the first statement, and discards the rest.
If you need to process multiple statements at a time, set a "sqlite_allow_multiple_statements" attribute
of a database handle to true when you connect to a database, and "do" method takes care of the rest
(since 1.30_01, and without creating DBI's statement handles internally since 1.47_01). If you do need to
use "prepare" or "prepare_cached" (which I don't recommend in this case, because typically there's no
placeholder nor reusable part in a dump), you can look at << $sth->{sqlite_unprepared_statements} >> to
retrieve what's left, though it usually contains nothing but white spaces.
Performance
SQLite is fast, very fast. Matt processed his 72MB log file with it, inserting the data (400,000+ rows)
by using transactions and only committing every 1000 rows (otherwise the insertion is quite slow), and
then performing queries on the data.
Queries like count(*) and avg(bytes) took fractions of a second to return, but what surprised him most of
all was:
SELECT url, count(*) as count
FROM access_log
GROUP BY url
ORDER BY count desc
LIMIT 20
To discover the top 20 hit URLs on the site (<http://axkit.org>), and it returned within 2 seconds. He
was seriously considering switching his log analysis code to use this little speed demon!
Oh yeah, and that was with no indexes on the table, on a 400MHz PIII.
For best performance be sure to tune your hdparm settings if you are using linux. Also you might want to
set:
PRAGMA synchronous = OFF
Which will prevent SQLite from doing fsync's when writing (which slows down non-transactional writes
significantly) at the expense of some peace of mind. Also try playing with the cache_size pragma.
The memory usage of SQLite can also be tuned using the cache_size pragma.
$dbh->do("PRAGMA cache_size = 800000");
The above will allocate 800M for DB cache; the default is 2M. Your sweet spot probably lies somewhere in
between.
DRIVER PRIVATE ATTRIBUTES
Database Handle Attributes
sqlite_version
Returns the version of the SQLite library which DBD::SQLite is using, e.g., "2.8.0". Can only be
read.
sqlite_unicode
If set to a true value, DBD::SQLite will turn the UTF-8 flag on for all text strings coming out of
the database (this feature is currently disabled for perl < 5.8.5). For more details on the UTF-8
flag see perlunicode. The default is for the UTF-8 flag to be turned off.
Also note that due to some bizarreness in SQLite's type system (see
<http://www.sqlite.org/datatype3.html>), if you want to retain blob-style behavior for some columns
under "$dbh->{sqlite_unicode} = 1" (say, to store images in the database), you have to state so
explicitly using the 3-argument form of "bind_param" in DBI when doing updates:
use DBI qw(:sql_types);
$dbh->{sqlite_unicode} = 1;
my $sth = $dbh->prepare("INSERT INTO mytable (blobcolumn) VALUES (?)");
# Binary_data will be stored as is.
$sth->bind_param(1, $binary_data, SQL_BLOB);
Defining the column type as "BLOB" in the DDL is not sufficient.
This attribute was originally named as "unicode", and renamed to "sqlite_unicode" for integrity since
version 1.26_06. Old "unicode" attribute is still accessible but will be deprecated in the near
future.
sqlite_allow_multiple_statements
If you set this to true, "do" method will process multiple statements at one go. This may be handy,
but with performance penalty. See above for details.
sqlite_use_immediate_transaction
If you set this to true, DBD::SQLite tries to issue a "begin immediate transaction" (instead of
"begin transaction") when necessary. See above for details.
As of version 1.38_01, this attribute is set to true by default. If you really need to use
"deferred" transactions for some reasons, set this to false explicitly.
sqlite_see_if_its_a_number
If you set this to true, DBD::SQLite tries to see if the bind values are number or not, and does not
quote if they are numbers. See above for details.
sqlite_extended_result_codes
If set to true, DBD::SQLite uses extended result codes where appropriate (see
<http://www.sqlite.org/rescode.html>).
Statement Handle Attributes
sqlite_unprepared_statements
Returns an unprepared part of the statement you pass to "prepare". Typically this contains nothing
but white spaces after a semicolon. See above for details.
METHODS
See also to the DBI documentation for the details of other common methods.
table_info
$sth = $dbh->table_info(undef, $schema, $table, $type, \%attr);
Returns all tables and schemas (databases) as specified in "table_info" in DBI. The schema and table
arguments will do a "LIKE" search. You can specify an ESCAPE character by including an 'Escape' attribute
in \%attr. The $type argument accepts a comma separated list of the following types 'TABLE', 'VIEW',
'LOCAL TEMPORARY' and 'SYSTEM TABLE' (by default all are returned). Note that a statement handle is
returned, and not a direct list of tables.
The following fields are returned:
TABLE_CAT: Always NULL, as SQLite does not have the concept of catalogs.
TABLE_SCHEM: The name of the schema (database) that the table or view is in. The default schema is
'main', temporary tables are in 'temp' and other databases will be in the name given when the database
was attached.
TABLE_NAME: The name of the table or view.
TABLE_TYPE: The type of object returned. Will be one of 'TABLE', 'VIEW', 'LOCAL TEMPORARY' or 'SYSTEM
TABLE'.
primary_key, primary_key_info
@names = $dbh->primary_key(undef, $schema, $table);
$sth = $dbh->primary_key_info(undef, $schema, $table, \%attr);
You can retrieve primary key names or more detailed information. As noted above, SQLite does not have
the concept of catalogs, so the first argument of the methods is usually "undef", and you'll usually set
"undef" for the second one (unless you want to know the primary keys of temporary tables).
foreign_key_info
$sth = $dbh->foreign_key_info(undef, $pk_schema, $pk_table,
undef, $fk_schema, $fk_table);
Returns information about foreign key constraints, as specified in "foreign_key_info" in DBI, but with
some limitations :
• information in rows returned by the $sth is incomplete with respect to the "foreign_key_info" in DBI
specification. All requested fields are present, but the content is "undef" for some of them.
The following nonempty fields are returned :
PKTABLE_NAME: The primary (unique) key table identifier.
PKCOLUMN_NAME: The primary (unique) key column identifier.
FKTABLE_NAME: The foreign key table identifier.
FKCOLUMN_NAME: The foreign key column identifier.
KEY_SEQ: The column sequence number (starting with 1), when several columns belong to a same constraint.
UPDATE_RULE: The referential action for the UPDATE rule. The following codes are defined:
CASCADE 0
RESTRICT 1
SET NULL 2
NO ACTION 3
SET DEFAULT 4
Default is 3 ('NO ACTION').
DELETE_RULE: The referential action for the DELETE rule. The codes are the same as for UPDATE_RULE.
Unfortunately, the DEFERRABILITY field is always "undef"; as a matter of fact, deferrability clauses are
supported by SQLite, but they can't be reported because the "PRAGMA foreign_key_list" tells nothing about
them.
UNIQUE_OR_PRIMARY: Whether the column is primary or unique.
Note: foreign key support in SQLite must be explicitly turned on through a "PRAGMA" command; see "Foreign
keys" earlier in this manual.
statistics_info
$sth = $dbh->statistics_info(undef, $schema, $table,
$unique_only, $quick);
Returns information about a table and it's indexes, as specified in "statistics_info" in DBI, but with
some limitations :
• information in rows returned by the $sth is incomplete with respect to the "statistics_info" in DBI
specification. All requested fields are present, but the content is "undef" for some of them.
The following nonempty fields are returned :
TABLE_SCHEM: The name of the schema (database) that the table is in. The default schema is 'main',
temporary tables are in 'temp' and other databases will be in the name given when the database was
attached.
TABLE_NAME: The name of the table
NON_UNIQUE: Contains 0 for unique indexes, 1 for non-unique indexes
INDEX_NAME: The name of the index
TYPE: SQLite uses 'btree' for all it's indexes
ORDINAL_POSITION: Column sequence number (starting with 1).
COLUMN_NAME: The name of the column
ping
my $bool = $dbh->ping;
returns true if the database file exists (or the database is in-memory), and the database connection is
active.
DRIVER PRIVATE METHODS
The following methods can be called via the func() method with a little tweak, but the use of func()
method is now discouraged by the DBI author for various reasons (see DBI's document
<http://search.cpan.org/dist/DBI/lib/DBI/DBD.pm#Using_install_method()_to_expose_driver-private_methods>
for details). So, if you're using DBI >= 1.608, use these "sqlite_" methods. If you need to use an older
DBI, you can call these like this:
$dbh->func( ..., "(method name without sqlite_ prefix)" );
Exception: "sqlite_trace" should always be called as is, even with "func()" method (to avoid conflict
with DBI's trace() method).
$dbh->func( ..., "sqlite_trace");
$dbh->sqlite_last_insert_rowid()
This method returns the last inserted rowid. If you specify an INTEGER PRIMARY KEY as the first column in
your table, that is the column that is returned. Otherwise, it is the hidden ROWID column. See the
SQLite docs for details.
Generally you should not be using this method. Use the DBI last_insert_id method instead. The usage of
this is:
$h->last_insert_id($catalog, $schema, $table_name, $field_name [, \%attr ])
Running "$h->last_insert_id("","","","")" is the equivalent of running "$dbh->sqlite_last_insert_rowid()"
directly.
$dbh->sqlite_db_filename()
Retrieve the current (main) database filename. If the database is in-memory or temporary, this returns
"undef".
$dbh->sqlite_busy_timeout()
Retrieve the current busy timeout.
$dbh->sqlite_busy_timeout( $ms )
Set the current busy timeout. The timeout is in milliseconds.
$dbh->sqlite_create_function( $name, $argc, $code_ref, $flags )
This method will register a new function which will be usable in an SQL query. The method's parameters
are:
$name
The name of the function. This is the name of the function as it will be used from SQL.
$argc
The number of arguments taken by the function. If this number is -1, the function can take any number
of arguments.
$code_ref
This should be a reference to the function's implementation.
$flags
You can optionally pass an extra flag bit to create_function, which then would be ORed with
SQLITE_UTF8 (default). As of 1.47_02 (SQLite 3.8.9), only meaning bit is SQLITE_DETERMINISTIC
(introduced at SQLite 3.8.3), which can make the function perform better. See C API documentation at
<http://sqlite.org/c3ref/create_function.html> for details.
For example, here is how to define a now() function which returns the current number of seconds since the
epoch:
$dbh->sqlite_create_function( 'now', 0, sub { return time } );
After this, it could be used from SQL as:
INSERT INTO mytable ( now() );
REGEXP function
SQLite includes syntactic support for an infix operator 'REGEXP', but without any implementation. The
"DBD::SQLite" driver automatically registers an implementation that performs standard perl regular
expression matching, using current locale. So for example you can search for words starting with an 'A'
with a query like
SELECT * from table WHERE column REGEXP '\bA\w+'
If you want case-insensitive searching, use perl regex flags, like this :
SELECT * from table WHERE column REGEXP '(?i:\bA\w+)'
The default REGEXP implementation can be overridden through the "create_function" API described above.
Note that regexp matching will not use SQLite indices, but will iterate over all rows, so it could be
quite costly in terms of performance.
$dbh->sqlite_create_collation( $name, $code_ref )
This method manually registers a new function which will be usable in an SQL query as a COLLATE option
for sorting. Such functions can also be registered automatically on demand: see section "COLLATION
FUNCTIONS" below.
The method's parameters are:
$name
The name of the function exposed to SQL.
$code_ref
Reference to the function's implementation. The driver will check that this is a proper sorting
function.
$dbh->sqlite_collation_needed( $code_ref )
This method manually registers a callback function that will be invoked whenever an undefined collation
sequence is required from an SQL statement. The callback is invoked as
$code_ref->($dbh, $collation_name)
and should register the desired collation using "sqlite_create_collation".
An initial callback is already registered by "DBD::SQLite", so for most common cases it will be simpler
to just add your collation sequences in the %DBD::SQLite::COLLATION hash (see section "COLLATION
FUNCTIONS" below).
$dbh->sqlite_create_aggregate( $name, $argc, $pkg, $flags )
This method will register a new aggregate function which can then be used from SQL. The method's
parameters are:
$name
The name of the aggregate function, this is the name under which the function will be available from
SQL.
$argc
This is an integer which tells the SQL parser how many arguments the function takes. If that number
is -1, the function can take any number of arguments.
$pkg
This is the package which implements the aggregator interface.
$flags
You can optionally pass an extra flag bit to create_aggregate, which then would be ORed with
SQLITE_UTF8 (default). As of 1.47_02 (SQLite 3.8.9), only meaning bit is SQLITE_DETERMINISTIC
(introduced at SQLite 3.8.3), which can make the function perform better. See C API documentation at
<http://sqlite.org/c3ref/create_function.html> for details.
The aggregator interface consists of defining three methods:
new()
This method will be called once to create an object which should be used to aggregate the rows in a
particular group. The step() and finalize() methods will be called upon the reference return by the
method.
step(@_)
This method will be called once for each row in the aggregate.
finalize()
This method will be called once all rows in the aggregate were processed and it should return the
aggregate function's result. When there is no rows in the aggregate, finalize() will be called right
after new().
Here is a simple aggregate function which returns the variance (example adapted from pysqlite):
package variance;
sub new { bless [], shift; }
sub step {
my ( $self, $value ) = @_;
push @$self, $value;
}
sub finalize {
my $self = $_[0];
my $n = @$self;
# Variance is NULL unless there is more than one row
return undef unless $n || $n == 1;
my $mu = 0;
foreach my $v ( @$self ) {
$mu += $v;
}
$mu /= $n;
my $sigma = 0;
foreach my $v ( @$self ) {
$sigma += ($v - $mu)**2;
}
$sigma = $sigma / ($n - 1);
return $sigma;
}
$dbh->sqlite_create_aggregate( "variance", 1, 'variance' );
The aggregate function can then be used as:
SELECT group_name, variance(score)
FROM results
GROUP BY group_name;
For more examples, see the DBD::SQLite::Cookbook.
$dbh->sqlite_progress_handler( $n_opcodes, $code_ref )
This method registers a handler to be invoked periodically during long running calls to SQLite.
An example use for this interface is to keep a GUI updated during a large query. The parameters are:
$n_opcodes
The progress handler is invoked once for every $n_opcodes virtual machine opcodes in SQLite.
$code_ref
Reference to the handler subroutine. If the progress handler returns non-zero, the SQLite operation
is interrupted. This feature can be used to implement a "Cancel" button on a GUI dialog box.
Set this argument to "undef" if you want to unregister a previous progress handler.
$dbh->sqlite_commit_hook( $code_ref )
This method registers a callback function to be invoked whenever a transaction is committed. Any callback
set by a previous call to "sqlite_commit_hook" is overridden. A reference to the previous callback (if
any) is returned. Registering an "undef" disables the callback.
When the commit hook callback returns zero, the commit operation is allowed to continue normally. If the
callback returns non-zero, then the commit is converted into a rollback (in that case, any attempt to
explicitly call "$dbh->rollback()" afterwards would yield an error).
$dbh->sqlite_rollback_hook( $code_ref )
This method registers a callback function to be invoked whenever a transaction is rolled back. Any
callback set by a previous call to "sqlite_rollback_hook" is overridden. A reference to the previous
callback (if any) is returned. Registering an "undef" disables the callback.
$dbh->sqlite_update_hook( $code_ref )
This method registers a callback function to be invoked whenever a row is updated, inserted or deleted.
Any callback set by a previous call to "sqlite_update_hook" is overridden. A reference to the previous
callback (if any) is returned. Registering an "undef" disables the callback.
The callback will be called as
$code_ref->($action_code, $database, $table, $rowid)
where
$action_code
is an integer equal to either "DBD::SQLite::INSERT", "DBD::SQLite::DELETE" or "DBD::SQLite::UPDATE"
(see "Action Codes");
$database
is the name of the database containing the affected row;
$table
is the name of the table containing the affected row;
$rowid
is the unique 64-bit signed integer key of the affected row within that table.
$dbh->sqlite_set_authorizer( $code_ref )
This method registers an authorizer callback to be invoked whenever SQL statements are being compiled by
the "prepare" in DBI method. The authorizer callback should return "DBD::SQLite::OK" to allow the
action, "DBD::SQLite::IGNORE" to disallow the specific action but allow the SQL statement to continue to
be compiled, or "DBD::SQLite::DENY" to cause the entire SQL statement to be rejected with an error. If
the authorizer callback returns any other value, then "prepare" call that triggered the authorizer will
fail with an error message.
An authorizer is used when preparing SQL statements from an untrusted source, to ensure that the SQL
statements do not try to access data they are not allowed to see, or that they do not try to execute
malicious statements that damage the database. For example, an application may allow a user to enter
arbitrary SQL queries for evaluation by a database. But the application does not want the user to be able
to make arbitrary changes to the database. An authorizer could then be put in place while the user-
entered SQL is being prepared that disallows everything except SELECT statements.
The callback will be called as
$code_ref->($action_code, $string1, $string2, $database, $trigger_or_view)
where
$action_code
is an integer that specifies what action is being authorized (see "Action Codes").
$string1, $string2
are strings that depend on the action code (see "Action Codes").
$database
is the name of the database ("main", "temp", etc.) if applicable.
$trigger_or_view
is the name of the inner-most trigger or view that is responsible for the access attempt, or "undef"
if this access attempt is directly from top-level SQL code.
$dbh->sqlite_backup_from_file( $filename )
This method accesses the SQLite Online Backup API, and will take a backup of the named database file,
copying it to, and overwriting, your current database connection. This can be particularly handy if your
current connection is to the special :memory: database, and you wish to populate it from an existing DB.
$dbh->sqlite_backup_to_file( $filename )
This method accesses the SQLite Online Backup API, and will take a backup of the currently connected
database, and write it out to the named file.
$dbh->sqlite_enable_load_extension( $bool )
Calling this method with a true value enables loading (external) SQLite3 extensions. After the call, you
can load extensions like this:
$dbh->sqlite_enable_load_extension(1);
$sth = $dbh->prepare("select load_extension('libsqlitefunctions.so')")
or die "Cannot prepare: " . $dbh->errstr();
$dbh->sqlite_load_extension( $file, $proc )
Loading an extension by a select statement (with the "load_extension" SQLite3 function like above) has
some limitations. If you need to, say, create other functions from an extension, use this method. $file
(a path to the extension) is mandatory, and $proc (an entry point name) is optional. You need to call
"sqlite_enable_load_extension" before calling "sqlite_load_extension".
$dbh->sqlite_trace( $code_ref )
This method registers a trace callback to be invoked whenever SQL statements are being run.
The callback will be called as
$code_ref->($statement)
where
$statement
is a UTF-8 rendering of the SQL statement text as the statement first begins executing.
Additional callbacks might occur as each triggered subprogram is entered. The callbacks for triggers
contain a UTF-8 SQL comment that identifies the trigger.
See also "TRACING" in DBI for better tracing options.
$dbh->sqlite_profile( $code_ref )
This method registers a profile callback to be invoked whenever a SQL statement finishes.
The callback will be called as
$code_ref->($statement, $elapsed_time)
where
$statement
is the original statement text (without bind parameters).
$elapsed_time
is an estimate of wall-clock time of how long that statement took to run (in milliseconds).
This method is considered experimental and is subject to change in future versions of SQLite.
See also DBI::Profile for better profiling options.
$dbh->sqlite_table_column_metadata( $dbname, $tablename, $columnname )
is for internal use only.
$dbh->sqlite_db_status()
Returns a hash reference that holds a set of status information of database connection such as cache
usage. See <http://www.sqlite.org/c3ref/c_dbstatus_options.html> for details. You may also pass 0 as an
argument to reset the status.
$sth->sqlite_st_status()
Returns a hash reference that holds a set of status information of SQLite statement handle such as full
table scan count. See <http://www.sqlite.org/c3ref/c_stmtstatus_counter.html> for details. Statement
status only holds the current value.
my $status = $sth->sqlite_st_status();
my $cur = $status->{fullscan_step};
You may also pass 0 as an argument to reset the status.
$dbh->sqlite_create_module()
Registers a name for a virtual table module. Module names must be registered before creating a new
virtual table using the module and before using a preexisting virtual table for the module. Virtual
tables are explained in DBD::SQLite::VirtualTable.
DRIVER FUNCTIONS
DBD::SQLite::compile_options()
Returns an array of compile options (available since SQLite 3.6.23, bundled in DBD::SQLite 1.30_01), or
an empty array if the bundled library is old or compiled with SQLITE_OMIT_COMPILEOPTION_DIAGS.
DBD::SQLite::sqlite_status()
Returns a hash reference that holds a set of status information of SQLite runtime such as memory usage or
page cache usage (see <http://www.sqlite.org/c3ref/c_status_malloc_count.html> for details). Each of the
entry contains the current value and the highwater value.
my $status = DBD::SQLite::sqlite_status();
my $cur = $status->{memory_used}{current};
my $high = $status->{memory_used}{highwater};
You may also pass 0 as an argument to reset the status.
DBD::SQLite::strlike($pattern, $string, $escape_char), DBD::SQLite::strglob($pattern, $string)
As of 1.49_05 (SQLite 3.10.0), you can use these two functions to see if a string matches a pattern.
These may be useful when you create a virtual table or a custom function. See
<http://sqlite.org/c3ref/strlike.html> and <http://sqlite.org/c3ref/strglob.html> for details.
DRIVER CONSTANTS
A subset of SQLite C constants are made available to Perl, because they may be needed when writing hooks
or authorizer callbacks. For accessing such constants, the "DBD::SQLite" module must be explicitly "use"d
at compile time. For example, an authorizer that forbids any DELETE operation would be written as follows
:
use DBD::SQLite;
$dbh->sqlite_set_authorizer(sub {
my $action_code = shift;
return $action_code == DBD::SQLite::DELETE ? DBD::SQLite::DENY
: DBD::SQLite::OK;
});
The list of constants implemented in "DBD::SQLite" is given below; more information can be found ad at
<http://www.sqlite.org/c3ref/constlist.html>.
Authorizer Return Codes
OK
DENY
IGNORE
Action Codes
The "set_authorizer" method registers a callback function that is invoked to authorize certain SQL
statement actions. The first parameter to the callback is an integer code that specifies what action is
being authorized. The second and third parameters to the callback are strings, the meaning of which
varies according to the action code. Below is the list of action codes, together with their associated
strings.
# constant string1 string2
# ======== ======= =======
CREATE_INDEX Index Name Table Name
CREATE_TABLE Table Name undef
CREATE_TEMP_INDEX Index Name Table Name
CREATE_TEMP_TABLE Table Name undef
CREATE_TEMP_TRIGGER Trigger Name Table Name
CREATE_TEMP_VIEW View Name undef
CREATE_TRIGGER Trigger Name Table Name
CREATE_VIEW View Name undef
DELETE Table Name undef
DROP_INDEX Index Name Table Name
DROP_TABLE Table Name undef
DROP_TEMP_INDEX Index Name Table Name
DROP_TEMP_TABLE Table Name undef
DROP_TEMP_TRIGGER Trigger Name Table Name
DROP_TEMP_VIEW View Name undef
DROP_TRIGGER Trigger Name Table Name
DROP_VIEW View Name undef
INSERT Table Name undef
PRAGMA Pragma Name 1st arg or undef
READ Table Name Column Name
SELECT undef undef
TRANSACTION Operation undef
UPDATE Table Name Column Name
ATTACH Filename undef
DETACH Database Name undef
ALTER_TABLE Database Name Table Name
REINDEX Index Name undef
ANALYZE Table Name undef
CREATE_VTABLE Table Name Module Name
DROP_VTABLE Table Name Module Name
FUNCTION undef Function Name
SAVEPOINT Operation Savepoint Name
COLLATION FUNCTIONS
Definition
SQLite v3 provides the ability for users to supply arbitrary comparison functions, known as user-defined
"collation sequences" or "collating functions", to be used for comparing two text values.
<http://www.sqlite.org/datatype3.html#collation> explains how collations are used in various SQL
expressions.
Builtin collation sequences
The following collation sequences are builtin within SQLite :
BINARY
Compares string data using memcmp(), regardless of text encoding.
NOCASE
The same as binary, except the 26 upper case characters of ASCII are folded to their lower case
equivalents before the comparison is performed. Note that only ASCII characters are case folded.
SQLite does not attempt to do full UTF case folding due to the size of the tables required.
RTRIM
The same as binary, except that trailing space characters are ignored.
In addition, "DBD::SQLite" automatically installs the following collation sequences :
perl
corresponds to the Perl "cmp" operator
perllocale
Perl "cmp" operator, in a context where "use locale" is activated.
Usage
You can write for example
CREATE TABLE foo(
txt1 COLLATE perl,
txt2 COLLATE perllocale,
txt3 COLLATE nocase
)
or
SELECT * FROM foo ORDER BY name COLLATE perllocale
Unicode handling
If the attribute "$dbh->{sqlite_unicode}" is set, strings coming from the database and passed to the
collation function will be properly tagged with the utf8 flag; but this only works if the
"sqlite_unicode" attribute is set before the first call to a perl collation sequence . The recommended
way to activate unicode is to set the parameter at connection time :
my $dbh = DBI->connect(
"dbi:SQLite:dbname=foo", "", "",
{
RaiseError => 1,
sqlite_unicode => 1,
}
);
Adding user-defined collations
The native SQLite API for adding user-defined collations is exposed through methods
"sqlite_create_collation" and "sqlite_collation_needed".
To avoid calling these functions every time a $dbh handle is created, "DBD::SQLite" offers a simpler
interface through the %DBD::SQLite::COLLATION hash : just insert your own collation functions in that
hash, and whenever an unknown collation name is encountered in SQL, the appropriate collation function
will be loaded on demand from the hash. For example, here is a way to sort text values regardless of
their accented characters :
use DBD::SQLite;
$DBD::SQLite::COLLATION{no_accents} = sub {
my ( $a, $b ) = map lc, @_;
tr[��������������������������
[aaaaaacdeeeeiiiinoooooouuuuy] for $a, $b;
$a cmp $b;
};
my $dbh = DBI->connect("dbi:SQLite:dbname=dbfile");
my $sql = "SELECT ... FROM ... ORDER BY ... COLLATE no_accents");
my $rows = $dbh->selectall_arrayref($sql);
The builtin "perl" or "perllocale" collations are predefined in that same hash.
The COLLATION hash is a global registry within the current process; hence there is a risk of undesired
side-effects. Therefore, to prevent action at distance, the hash is implemented as a "write-only" hash,
that will happily accept new entries, but will raise an exception if any attempt is made to override or
delete a existing entry (including the builtin "perl" and "perllocale").
If you really, really need to change or delete an entry, you can always grab the tied object underneath
%DBD::SQLite::COLLATION --- but don't do that unless you really know what you are doing. Also observe
that changes in the global hash will not modify existing collations in existing database handles: it will
only affect new requests for collations. In other words, if you want to change the behaviour of a
collation within an existing $dbh, you need to call the "create_collation" method directly.
FULLTEXT SEARCH
SQLite is bundled with an extension module for full-text indexing. Tables with this feature enabled can
be efficiently queried to find rows that contain one or more instances of some specified words, in any
column, even if the table contains many large documents.
Explanations for using this feature are provided in a separate document: see
DBD::SQLite::Fulltext_search.
R* TREE SUPPORT
The RTREE extension module within SQLite adds support for creating a R-Tree, a special index for range
and multidimensional queries. This allows users to create tables that can be loaded with (as an example)
geospatial data such as latitude/longitude coordinates for buildings within a city :
CREATE VIRTUAL TABLE city_buildings USING rtree(
id, -- Integer primary key
minLong, maxLong, -- Minimum and maximum longitude
minLat, maxLat -- Minimum and maximum latitude
);
then query which buildings overlap or are contained within a specified region:
# IDs that are contained within query coordinates
my $contained_sql = <<"";
SELECT id FROM city_buildings
WHERE minLong >= ? AND maxLong <= ?
AND minLat >= ? AND maxLat <= ?
# ... and those that overlap query coordinates
my $overlap_sql = <<"";
SELECT id FROM city_buildings
WHERE maxLong >= ? AND minLong <= ?
AND maxLat >= ? AND minLat <= ?
my $contained = $dbh->selectcol_arrayref($contained_sql,undef,
$minLong, $maxLong, $minLat, $maxLat);
my $overlapping = $dbh->selectcol_arrayref($overlap_sql,undef,
$minLong, $maxLong, $minLat, $maxLat);
For more detail, please see the SQLite R-Tree page (<http://www.sqlite.org/rtree.html>). Note that custom
R-Tree queries using callbacks, as mentioned in the prior link, have not been implemented yet.
VIRTUAL TABLES IMPLEMENTED IN PERL
SQLite has a concept of "virtual tables" which look like regular tables but are implemented internally
through specific functions. The fulltext or R* tree features described in the previous chapters are
examples of such virtual tables, implemented in C code.
"DBD::SQLite" also supports virtual tables implemented in Perl code: see DBD::SQLite::VirtualTable for
using or implementing such virtual tables. These can have many interesting uses for joining regular DBMS
data with some other kind of data within your Perl programs. Bundled with the present distribution are :
• DBD::SQLite::VirtualTable::FileContent : implements a virtual column that exposes file contents. This
is especially useful in conjunction with a fulltext index; see DBD::SQLite::Fulltext_search.
• DBD::SQLite::VirtualTable::PerlData : binds to a Perl array within the Perl program. This can be used
for simple import/export operations, for debugging purposes, for joining data from different sources,
etc.
Other Perl virtual tables may also be published separately on CPAN.
FOR DBD::SQLITE EXTENSION AUTHORS
Since 1.30_01, you can retrieve the bundled SQLite C source and/or header like this:
use File::ShareDir 'dist_dir';
use File::Spec::Functions 'catfile';
# the whole sqlite3.h header
my $sqlite3_h = catfile(dist_dir('DBD-SQLite'), 'sqlite3.h');
# or only a particular header, amalgamated in sqlite3.c
my $what_i_want = 'parse.h';
my $sqlite3_c = catfile(dist_dir('DBD-SQLite'), 'sqlite3.c');
open my $fh, '<', $sqlite3_c or die $!;
my $code = do { local $/; <$fh> };
my ($parse_h) = $code =~ m{(
/\*+[ ]Begin[ ]file[ ]$what_i_want[ ]\*+
.+?
/\*+[ ]End[ ]of[ ]$what_i_want[ ]\*+/
)}sx;
open my $out, '>', $what_i_want or die $!;
print $out $parse_h;
close $out;
You usually want to use this in your extension's "Makefile.PL", and you may want to add DBD::SQLite to
your extension's "CONFIGURE_REQUIRES" to ensure your extension users use the same C source/header they
use to build DBD::SQLite itself (instead of the ones installed in their system).
TO DO
The following items remain to be done.
Leak Detection
Implement one or more leak detection tests that only run during AUTOMATED_TESTING and RELEASE_TESTING and
validate that none of the C code we work with leaks.
Stream API for Blobs
Reading/writing into blobs using "sqlite2_blob_open" / "sqlite2_blob_close".
Support for custom callbacks for R-Tree queries
Custom queries of a R-Tree index using a callback are possible with the SQLite C API
(<http://www.sqlite.org/rtree.html>), so one could potentially use a callback that narrowed the result
set down based on a specific need, such as querying for overlapping circles.
SUPPORT
Bugs should be reported via the CPAN bug tracker at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBD-SQLite>
Note that bugs of bundled SQLite library (i.e. bugs in "sqlite3.[ch]") should be reported to the SQLite
developers at sqlite.org via their bug tracker or via their mailing list.
The master repository is on GitHub:
<https://github.com/DBD-SQLite/DBD-SQLite>.
We also have a mailing list:
<http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbd-sqlite>
AUTHORS
Matt Sergeant <matt@sergeant.org>
Francis J. Lacoste <flacoste@logreport.org>
Wolfgang Sourdeau <wolfgang@logreport.org>
Adam Kennedy <adamk@cpan.org>
Max Maischein <corion@cpan.org>
Laurent Dami <dami@cpan.org>
Kenichi Ishigaki <ishigaki@cpan.org>
COPYRIGHT
The bundled SQLite code in this distribution is Public Domain.
DBD::SQLite is copyright 2002 - 2007 Matt Sergeant.
Some parts copyright 2008 Francis J. Lacoste.
Some parts copyright 2008 Wolfgang Sourdeau.
Some parts copyright 2008 - 2013 Adam Kennedy.
Some parts copyright 2009 - 2013 Kenichi Ishigaki.
Some parts derived from DBD::SQLite::Amalgamation copyright 2008 Audrey Tang.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl
itself.
The full text of the license can be found in the LICENSE file included with this module.