bionic (3) tdbc_statement.3tcl.gz
NAME
tdbc::statement - TDBC statement object
SYNOPSIS
package require tdbc 1.0
package require tdbc::driver version
tdbc::driver::connection create db ?-option value...?
set stmt [db prepare sql-code]
set stmt [db preparecall call]
$stmt params
$stmt paramtype ?direction? type ?precision? ?scale?
$stmt execute ?dict?
$stmt resultsets
$stmt allrows ?-as lists|dicts? ?-columnsvariable name? ?--? ?dict
$stmt foreach ?-as lists|dicts? ?-columnsvariable name? ?--? varName ?dict? script
$stmt close
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DESCRIPTION
Every database driver for TDBC (Tcl DataBase Connectivity) implements a statement object that represents
a SQL statement in a database. Instances of this object are created by executing the prepare or
preparecall object command on a database connection.
The prepare object command against the connection accepts arbitrary SQL code to be executed against the
database. The SQL code may contain bound variables, which are strings of alphanumeric characters or
underscores (the first character of the string may not be numeric), prefixed with a colon (:). If a bound
variable appears in the SQL statement, and is not in a string set off by single or double quotes, nor in
a comment introduced by --, it becomes a value that is substituted when the statement is executed. A
bound variable becomes a single value (string or numeric) in the resulting statement. Drivers are
responsible for ensuring that the mechanism for binding variables prevents SQL injection.
The preparecall object command against the connection accepts a stylized statement in the form:
procname (?:varname? ?,:varname...?)
or
varname = procname (?:varname? ?,:varname...?)
This statement represents a call to a stored procedure procname in the database. The variable name to the
left of the equal sign (if present), and all variable names that are parameters inside parentheses,
become bound variables.
The params method against a statement object enumerates the bound variables that appear in the statement.
The result returned from the params method is a dictionary whose keys are the names of bound variables
(listed in the order in which the variables first appear in the statement), and whose values are
dictionaries. The subdictionaries include at least the following keys (database drivers may add
additional keys that are not in this list).
direction
Contains one of the keywords, in, out or inout according to whether the variable is an input to or
output from the statement. Only stored procedure calls will have out or inout parameters.
type Contains the data type of the column, and will generally be chosen from the set, bigint, binary,
bit, char, date, decimal, double, float, integer, longvarbinary, longvarchar, numeric, real, time,
timestamp, smallint, tinyint, varbinary, and varchar. (If the variable has a type that cannot be
represented as one of the above, type will contain a driver-dependent description of the type.)
precision
Contains the precision of the column in bits, decimal digits, or the width in characters,
according to the type.
scale Contains the scale of the column (the number of digits after the radix point), for types that
support the concept.
nullable
Contains 1 if the column can contain NULL values, and 0 otherwise.
The paramtype object command allows the script to specify the type and direction of parameter
transmission of a variable in a statement. (Some databases provide no method to determine this
information automatically and place the burden on the caller to do so.) The direction, type, precision,
scale, and nullable arguments have the same meaning as the corresponding dictionary values in the params
object command.
The execute object command executes the statement. Prior to executing the statement, values are provided
for the bound variables that appear in it. If the dict parameter is supplied, it is searched for a key
whose name matches the name of the bound variable. If the key is present, its value becomes the
substituted variable. If not, the value of the substituted variable becomes a SQL NULL. If the dict
parameter is not supplied, the execute object command searches for a variable in the caller's scope whose
name matches the name of the bound variable. If one is found, its value becomes the bound variable's
value. If none is found, the bound variable is assigned a SQL NULL as its value. Once substitution is
finished, the resulting statement is executed. The return value is a result set object (see
tdbc::resultset for details).
The resultsets method returns a list of all the result sets that have been returned by executing the
statement and have not yet been closed.
The allrows object command executes the statement as with the execute object command, accepting an
optional dict parameter giving bind variables. After executing the statement, it uses the allrows object
command on the result set (see tdbc::resultset) to construct a list of the results. Finally, the result
set is closed. The return value is the list of results.
The foreach object command executes the statement as with the execute object command, accepting an
optional dict parameter giving bind variables. After executing the statement, it uses the foreach object
command on the result set (see tdbc::resultset) to evaluate the given script for each row of the results.
Finally, the result set is closed, even if the given script results in a return, an error, or an unusual
return code.
The close object command removes a statement and any result sets that it has created. All system
resources associated with the objects are freed.
EXAMPLES
The following code would look up a telephone number in a directory, assuming an appropriate SQL schema:
package require tdbc::sqlite3
tdbc::sqlite3::connection create db phonebook.sqlite3
set statement [db prepare {
select phone_num from directory
where first_name = :firstname and last_name = :lastname
}]
set firstname Fred
set lastname Flintstone
$statement foreach row {
puts [dict get $row phone_num]
}
$statement close
db close
SEE ALSO
encoding(3tcl), tdbc(3tcl), tdbc::connection(3tcl), tdbc::resultset(3tcl), tdbc::tokenize(3tcl)
KEYWORDS
TDBC, SQL, database, connectivity, connection, resultset, statement, bound variable, stored procedure,
call
COPYRIGHT
Copyright (c) 2008 by Kevin B. Kenny.