<!--
-$PostgreSQL: pgsql/doc/src/sgml/plhandler.sgml,v 1.2 2003/11/29 19:51:37 pgsql Exp $
+$PostgreSQL: pgsql/doc/src/sgml/plhandler.sgml,v 1.3 2004/12/30 21:45:36 tgl Exp $
-->
<chapter id="plhandler">
</programlisting>
</para>
+ <para>
+ The procedural languages included in the standard distribution
+ are good references when trying to write your own call handler.
+ Look into the <filename>src/pl</> subdirectory of the source tree.
+ </para>
+
</chapter>
<!-- Keep this comment at the end of the file
<!--
-$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.34 2004/12/13 18:05:08 petere Exp $
+$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.35 2004/12/30 21:45:36 tgl Exp $
-->
<chapter id="plperl">
return $emp->{basesalary} + $emp->{bonus};
$$ LANGUAGE plperl;
-SELECT name, empcomp(employee) FROM employee;
+SELECT name, empcomp(employee.*) FROM employee;
</programlisting>
</para>
+
+ <para>
+ A PL/Perl function can return a composite-type result using the same
+ approach: return a reference to a hash that has the required attributes.
+ For example,
+
+<programlisting>
+CREATE TYPE testrowperl AS (f1 integer, f2 text, f3 text);
+
+CREATE OR REPLACE FUNCTION perl_row() RETURNS testrowperl AS $$
+ return {f2 => 'hello', f1 => 1, f3 => 'world'};
+$$ LANGUAGE plperl;
+
+SELECT * FROM perl_row();
+</programlisting>
+
+ Any columns in the declared result data type that are not present in the
+ hash will be returned as NULLs.
+ </para>
+
+ <para>
+ PL/Perl functions can also return sets of either scalar or composite
+ types. To do this, return a reference to an array that contains
+ either scalars or references to hashes, respectively. Here are
+ some simple examples:
+
+<programlisting>
+CREATE OR REPLACE FUNCTION perl_set_int(int) RETURNS SETOF INTEGER AS $$
+return [0..$_[0]];
+$$ LANGUAGE plperl;
+
+SELECT * FROM perl_set_int(5);
+
+
+CREATE OR REPLACE FUNCTION perl_set() RETURNS SETOF testrowperl AS $$
+ return [
+ { f1 => 1, f2 => 'Hello', f3 => 'World' },
+ { f1 => 2, f2 => 'Hello', f3 => 'PostgreSQL' },
+ { f1 => 3, f2 => 'Hello', f3 => 'PL/Perl' }
+ ];
+$$ LANGUAGE plperl;
+
+SELECT * FROM perl_set();
+</programlisting>
+
+ Note that when you do this, Perl will have to build the entire array in
+ memory; therefore the technique does not scale to very large result sets.
+ </para>
+
+ <para>
+ <application>PL/Perl</> does not currently have full support for
+ domain types: it treats a domain the same as the underlying scalar
+ type. This means that constraints associated with the domain will
+ not be enforced. This is not an issue for function arguments, but
+ it is a hazard if you declare a <application>PL/Perl</> function
+ as returning a domain type.
+ </para>
</sect1>
<sect1 id="plperl-database">
$nrows = $rv->{processed};
</programlisting>
</para>
+
+ <para>
+ Here is a complete example:
+<programlisting>
+CREATE TABLE test (
+ i int,
+ v varchar
+);
+
+INSERT INTO test (i, v) VALUES (1, 'first line');
+INSERT INTO test (i, v) VALUES (2, 'second line');
+INSERT INTO test (i, v) VALUES (3, 'third line');
+INSERT INTO test (i, v) VALUES (4, 'immortal');
+
+CREATE FUNCTION test_munge() RETURNS SETOF test AS $$
+ my $res = [];
+ my $rv = spi_exec_query('select i, v from test;');
+ my $status = $rv->{status};
+ my $nrows = $rv->{processed};
+ foreach my $rn (0 .. $nrows - 1) {
+ my $row = $rv->{rows}[$rn];
+ $row->{i} += 200 if defined($row->{i});
+ $row->{v} =~ tr/A-Za-z/a-zA-Z/ if (defined($row->{v}));
+ push @$res, $row;
+ }
+ return $res;
+$$ LANGUAGE plperl;
+
+SELECT * FROM test_munge();
+</programlisting>
+ </para>
</listitem>
</varlistentry>
Perl code, the error propagates out to the calling query, causing
the current transaction or subtransaction to be aborted. This
is effectively the same as the Perl <literal>die</> command.
- The other levels simply report the message to the system log
- and/or client.
+ The other levels only generate messages of different
+ priority levels.
+ Whether messages of a particular priority are reported to the client,
+ written to the server log, or both is controlled by the
+ <xref linkend="guc-log-min-messages"> and
+ <xref linkend="guc-client-min-messages"> configuration
+ variables. See <xref linkend="runtime-config"> for more
+ information.
</para>
</listitem>
</varlistentry>
had been displayed by a <command>SELECT</command> statement).
Conversely, the <literal>return</> command will accept any string
that is acceptable input format for the function's declared return
- type. So, the PL/Perl programmer can manipulate data values as if
- they were just text.
- </para>
-
- <para>
- PL/Perl can also return row sets and composite types, and row sets
- of composite types. Here is an example of a PL/Perl function
- returning a row set of a row type. Note that a composite type is
- always represented as a hash reference.
-<programlisting>
-CREATE TABLE test (
- i int,
- v varchar
-);
-
-INSERT INTO test (i, v) VALUES (1, 'first line');
-INSERT INTO test (i, v) VALUES (2, 'second line');
-INSERT INTO test (i, v) VALUES (3, 'third line');
-INSERT INTO test (i, v) VALUES (4, 'immortal');
-
-CREATE FUNCTION test_munge() RETURNS SETOF test AS $$
- my $res = [];
- my $rv = spi_exec_query('select i, v from test;');
- my $status = $rv->{status};
- my $nrows = $rv->{processed};
- foreach my $rn (0 .. $nrows - 1) {
- my $row = $rv->{rows}[$rn];
- $row->{i} += 200 if defined($row->{i});
- $row->{v} =~ tr/A-Za-z/a-zA-Z/ if (defined($row->{v}));
- push @$res, $row;
- }
- return $res;
-$$ LANGUAGE plperl;
-
-SELECT * FROM test_munge();
-</programlisting>
- </para>
-
- <para>
- Here is an example of a PL/Perl function returning a composite
- type:
-<programlisting>
-CREATE TYPE testrowperl AS (f1 integer, f2 text, f3 text);
-
-CREATE OR REPLACE FUNCTION perl_row() RETURNS testrowperl AS $$
- return {f2 => 'hello', f1 => 1, f3 => 'world'};
-$$ LANGUAGE plperl;
-</programlisting>
- </para>
-
- <para>
- Here is an example of a PL/Perl function returning a row set of a
- composite type. Since a row set is always a reference to an array
- and a composite type is always a reference to a hash, a row set of a
- composite type is a reference to an array of hash references.
-<programlisting>
-CREATE TYPE testsetperl AS (f1 integer, f2 text, f3 text);
-
-CREATE OR REPLACE FUNCTION perl_set() RETURNS SETOF testsetperl AS $$
- return [
- { f1 => 1, f2 => 'Hello', f3 => 'World' },
- { f1 => 2, f2 => 'Hello', f3 => 'PostgreSQL' },
- { f1 => 3, f2 => 'Hello', f3 => 'PL/Perl' }
- ];
-$$ LANGUAGE plperl;
-</programlisting>
+ type. So, within the PL/Perl function,
+ all values are just text strings.
</para>
</sect1>
<para>
You can use the global hash <varname>%_SHARED</varname> to store
data, including code references, between function calls for the
- lifetime of the current session, which is bounded from below by
- the lifetime of the current transaction.
+ lifetime of the current session.
</para>
<para>
CREATE OR REPLACE FUNCTION use_quote(TEXT) RETURNS text AS $$
my $text_to_quote = shift;
my $qfunc = $_SHARED{myquote};
- return &$qfunc($text_to_quote);
+ return &$qfunc($text_to_quote);
$$ LANGUAGE plperl;
</programlisting>
(You could have replaced the above with the one-liner
- <literal>return $_SHARED{myquote}->($_[0]);</literal>
+ <literal>return $_SHARED{myquote}->($_[0]);</literal>
at the expense of readability.)
</para>
</sect1>
<para>
In the current implementation, if you are fetching or returning
very large data sets, you should be aware that these will all go
- into memory. Future features will help with this. In the
- meantime, we suggest that you not use PL/Perl if you will fetch
- or return very large result sets.
+ into memory.
</para>
</listitem>
</itemizedlist>
<!--
-$PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.53 2004/12/19 22:10:41 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.54 2004/12/30 21:45:36 tgl Exp $
-->
<chapter id="plpgsql">
<para>
<acronym>SQL</acronym> is the language <productname>PostgreSQL</>
- (and most other relational databases) use as query language. It's
+ and most other relational databases use as query language. It's
portable and easy to learn. But every <acronym>SQL</acronym>
statement must be executed individually by the database server.
</para>
Finally, a <application>PL/pgSQL</> function may be declared to return
<type>void</> if it has no useful return value.
</para>
+
+ <para>
+ <application>PL/pgSQL</> does not currently have full support for
+ domain types: it treats a domain the same as the underlying scalar
+ type. This means that constraints associated with the domain will
+ not be enforced. This is not an issue for function arguments, but
+ it is a hazard if you declare a <application>PL/pgSQL</> function
+ as returning a domain type.
+ </para>
</sect2>
</sect1>
the code can become downright incomprehensible, because you can
easily find yourself needing half a dozen or more adjacent quote marks.
It's recommended that you instead write the function body as a
- <quote>dollar-quoted</> string literal. In the dollar-quoting
+ <quote>dollar-quoted</> string literal (see <xref
+ linkend="sql-syntax-dollar-quoting">). In the dollar-quoting
approach, you never double any quote marks, but instead take care to
choose a different dollar-quoting delimiter for each level of
nesting you need. For example, you might write the <command>CREATE
<para>
Each declaration and each statement within a block is terminated
- by a semicolon, although the final <literal>END</literal> that
- concludes a function body does not require one.
+ by a semicolon. A block that appears within another block must
+ have a semicolon after <literal>END</literal>, as shown above;
+ however the final <literal>END</literal> that
+ concludes a function body does not require a semicolon.
</para>
<para>
transaction, since there would be no context for them to execute in.
However, a block containing an <literal>EXCEPTION</> clause effectively
forms a subtransaction that can be rolled back without affecting the
- outer transaction. For more details see <xref
+ outer transaction. For more about that see <xref
linkend="plpgsql-error-trapping">.
</para>
</sect1>
<para>
The default value is evaluated every time the block is entered. So,
- for example, assigning <literal>'now'</literal> to a variable of type
+ for example, assigning <literal>now()</literal> to a variable of type
<type>timestamp</type> causes the variable to have the
time of the current function call, not the time when the function was
precompiled.
<literal>$<replaceable>n</replaceable></literal>
parameter names for increased readability. Either the alias or the
numeric identifier can then be used to refer to the parameter value.
+ </para>
+
+ <para>
There are two ways to create an alias. The preferred way is to give a
name to the parameter in the <command>CREATE FUNCTION</command> command,
for example:
<para>
All expressions used in <application>PL/pgSQL</application>
statements are processed using the server's regular
- <acronym>SQL</acronym> executor. Expressions that appear to
- contain constants may in fact require run-time evaluation
- (e.g., <literal>'now'</literal> for the <type>timestamp</type>
- type) so it is impossible for the
- <application>PL/pgSQL</application> parser to identify real
- constant values other than the key word <literal>NULL</>. All expressions are
- evaluated internally by executing a query
+ <acronym>SQL</acronym> executor. In effect, a query like
<synopsis>
SELECT <replaceable>expression</replaceable>
</synopsis>
- using the <acronym>SPI</acronym> manager. For evaluation,
+ is executed using the <acronym>SPI</acronym> manager. Before evaluation,
occurrences of <application>PL/pgSQL</application> variable
identifiers are replaced by parameters, and the actual values from
the variables are passed to the executor in the parameter array.
</para>
<para>
+ The <literal>INTO</> clause can appear almost anywhere in the
+ <command>SELECT</command> statement. Customarily it is written
+ either just after <literal>SELECT</> as shown above, or
+ just before <literal>FROM</> — that is, either just before
+ or just after the list of <replaceable>select_expressions</replaceable>.
+ </para>
+
+ <para>
If the query returns zero rows, null values are assigned to the
target(s). If the query returns multiple rows, the first
row is assigned to the target(s) and the rest are discarded.
</para>
<para>
- The <literal>INTO</> clause can appear almost anywhere in the <command>SELECT</command>
- statement.
- </para>
-
- <para>
- You can use <literal>FOUND</literal> immediately after a <command>SELECT
- INTO</command> statement to determine whether the assignment was successful
- (that is, at least one row was was returned by the query). For example:
+ You can check the special <literal>FOUND</literal> variable (see
+ <xref linkend="plpgsql-statements-diagnostics">) after a
+ <command>SELECT INTO</command> statement to determine whether the
+ assignment was successful, that is, at least one row was was returned by
+ the query. For example:
<programlisting>
SELECT INTO myrec * FROM emp WHERE empname = myname;
</para>
<para>
- When working with dynamic commands you will often have to handle escaping
- of single quotes. The recommended method for quoting fixed text in your
- function body is dollar quoting. If you have legacy code that does
- not use dollar quoting, please refer to the
- overview in <xref linkend="plpgsql-quote-tips">, which can save you
- some effort when translating said code to a more reasonable scheme.
- </para>
-
- <para>
Unlike all other commands in <application>PL/pgSQL</>, a command
run by an <command>EXECUTE</command> statement is not prepared
and saved just once during the life of the session. Instead, the
command is prepared each time the statement is run. The command
string can be dynamically created within the function to perform
- actions on variable tables and columns.
+ actions on different tables and columns.
</para>
<para>
</para>
<para>
+ When working with dynamic commands you will often have to handle escaping
+ of single quotes. The recommended method for quoting fixed text in your
+ function body is dollar quoting. (If you have legacy code that does
+ not use dollar quoting, please refer to the
+ overview in <xref linkend="plpgsql-quote-tips">, which can save you
+ some effort when translating said code to a more reasonable scheme.)
+ </para>
+
+ <para>
+ Dynamic values that are to be inserted into the constructed
+ query require special handling since they might themselves contain
+ quote characters.
An example (this assumes that you are using dollar quoting for the
function as a whole, so the quote marks need not be doubled):
<programlisting>
all three variants of the <command>FOR</> statement (integer
<command>FOR</> loops, record-set <command>FOR</> loops, and
dynamic record-set <command>FOR</>
- loops). <literal>FOUND</literal> is only set when the
- <command>FOR</> loop exits: inside the execution of the loop,
+ loops). <literal>FOUND</literal> is set this way when the
+ <command>FOR</> loop exits; inside the execution of the loop,
<literal>FOUND</literal> is not modified by the
<command>FOR</> statement, although it may be changed by the
execution of other statements within the loop body.
</para>
</listitem>
</itemizedlist>
- <literal>FOUND</literal> is a local variable; any changes
- to it affect only the current <application>PL/pgSQL</application>
- function.
+
+ <literal>FOUND</literal> is a local variable within each
+ <application>PL/pgSQL</application> function; so any changes
+ to it affect only the current function.
</para>
</sect2>
SELECT * FROM some_func();
</programlisting>
- That is, the function is used as a table source in a <literal>FROM</literal>
- clause.
+ That is, the function must be used as a table source in a
+ <literal>FROM</literal> clause.
</para>
<para>
<command>RETURN NEXT</command> does not actually return from the
- function; it simply saves away the value of the expression (or
- record or row variable, as appropriate for the data type being
- returned). Execution then continues with the next statement in
+ function; it simply saves away the value of the expression.
+ Execution then continues with the next statement in
the <application>PL/pgSQL</> function. As successive
<command>RETURN NEXT</command> commands are executed, the result
set is built up. A final <command>RETURN</command>, which should
BEGIN
-- some computations
IF stocks > 100000 THEN
- EXIT; -- invalid; cannot use EXIT outside of LOOP
+ EXIT; -- causes exit from the BEGIN block
END IF;
END;
</programlisting>
END LOOP;
</synopsis>
The record or row variable is successively assigned each row
- resulting from the query (which must be a <command>SELECT</command>
- command) and the loop body is executed for each row. Here is an example:
+ resulting from the <replaceable>query</replaceable> (which must be a
+ <command>SELECT</command> command) and the loop body is executed for each
+ row. Here is an example:
<programlisting>
CREATE FUNCTION cs_refresh_mviews() RETURNS integer AS $$
DECLARE
<literal>IN</> and <literal>LOOP</>. If <literal>..</> is not seen then
the loop is presumed to be a loop over rows. Mistyping the <literal>..</>
is thus likely to lead to a complaint along the lines of
- <quote>loop variable of loop over rows must be a record or row</>,
+ <quote>loop variable of loop over rows must be a record or row variable</>,
rather than the simple syntax error one might expect to get.
</para>
</note>
<replaceable>handler_statements</replaceable>
<optional> WHEN <replaceable>condition</replaceable> <optional> OR <replaceable>condition</replaceable> ... </optional> THEN
<replaceable>handler_statements</replaceable>
- ... </optional>
+ ... </optional>
END;
</synopsis>
</para>
<title><command>OPEN FOR SELECT</command></title>
<synopsis>
-OPEN <replaceable>unbound-cursor</replaceable> FOR SELECT ...;
+OPEN <replaceable>unbound_cursor</replaceable> FOR SELECT ...;
</synopsis>
<para>
<title><command>OPEN FOR EXECUTE</command></title>
<synopsis>
-OPEN <replaceable>unbound-cursor</replaceable> FOR EXECUTE <replaceable class="command">query-string</replaceable>;
+OPEN <replaceable>unbound_cursor</replaceable> FOR EXECUTE <replaceable class="command">query_string</replaceable>;
</synopsis>
<para>
<title>Opening a Bound Cursor</title>
<synopsis>
-OPEN <replaceable>bound-cursor</replaceable> <optional> ( <replaceable>argument_values</replaceable> ) </optional>;
+OPEN <replaceable>bound_cursor</replaceable> <optional> ( <replaceable>argument_values</replaceable> ) </optional>;
</synopsis>
<para>
priority levels.
Whether messages of a particular priority are reported to the client,
written to the server log, or both is controlled by the
- <varname>log_min_messages</varname> and
- <varname>client_min_messages</varname> configuration
+ <xref linkend="guc-log-min-messages"> and
+ <xref linkend="guc-client-min-messages"> configuration
variables. See <xref linkend="runtime-config"> for more
information.
</para>
<para>
Another way to log changes to a table involves creating a new table that
- holds a row for each insert, update, delete that occurs. This approach can
- be thought of as auditing changes to a table.
- </para>
-
- <para>
+ holds a row for each insert, update, or delete that occurs. This approach
+ can be thought of as auditing changes to a table.
<xref linkend="plpgsql-trigger-audit-example"> shows an example of an
audit trigger procedure in <application>PL/pgSQL</application>.
</para>
salary integer
);
-CREATE OR REPLACE FUNCTION process_emp_audit() RETURNS TRIGGER AS $emp_audit$
+CREATE OR REPLACE FUNCTION process_emp_audit() RETURNS TRIGGER AS $emp_audit$
BEGIN
--
-- Create a row in emp_audit to reflect the operation performed on emp,
INSERT INTO emp_audit SELECT 'I', now(), user, NEW.*;
RETURN NEW;
END IF;
+ RETURN NULL; -- result is ignored since this is an AFTER trigger
END;
$emp_audit$ language plpgsql;
-
CREATE TRIGGER emp_audit
AFTER INSERT OR UPDATE OR DELETE ON emp
- FOR EACH ROW EXECUTE PROCEDURE process_emp_audit()
-;
+ FOR EACH ROW EXECUTE PROCEDURE process_emp_audit();
</programlisting>
</example>
</sect1>
-<!-- $PostgreSQL: pgsql/doc/src/sgml/plpython.sgml,v 1.25 2004/12/17 02:14:44 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/plpython.sgml,v 1.26 2004/12/30 21:45:36 tgl Exp $ -->
<chapter id="plpython">
<title>PL/Python - Python Procedural Language</title>
<title>PL/Python Functions</title>
<para>
- The Python code you write gets transformed into a Python function.
- For example,
+ Functions in PL/Python are declared in the usual way, for example
<programlisting>
CREATE FUNCTION myfunc(text) RETURNS text
AS 'return args[0]'
LANGUAGE plpythonu;
</programlisting>
- gets transformed into
+ The Python code that is given as the body of the function definition
+ gets transformed into a Python function.
+ For example, the above results in
<programlisting>
def __plpython_procedure_myfunc_23456():
<literal>plpy.notice(<replaceable>msg</>)</literal>,
<literal>plpy.warning(<replaceable>msg</>)</literal>,
<literal>plpy.error(<replaceable>msg</>)</literal>, and
- <literal>plpy.fatal(<replaceable>msg</>)</literal>.
- These are mostly equivalent to calling
- <literal>elog(<replaceable>level</>, <replaceable>msg</>)</literal>
- from C code.<indexterm><primary>elog</><secondary>in
- PL/Python</></indexterm> <function>plpy.error</function> and
+ <literal>plpy.fatal(<replaceable>msg</>)</literal>.<indexterm><primary>elog</><secondary>in PL/Python</></indexterm>
+ <function>plpy.error</function> and
<function>plpy.fatal</function> actually raise a Python exception
- which, if uncaught, causes the PL/Python module to call
- <literal>elog(ERROR, msg)</literal> when the function handler
- returns from the Python interpreter. <literal>raise
- plpy.ERROR(<replaceable>msg</>)</literal> and <literal>raise
- plpy.FATAL(<replaceable>msg</>)</literal> are equivalent to calling
+ which, if uncaught, propagates out to the calling query, causing
+ the current transaction or subtransaction to be aborted.
+ <literal>raise plpy.ERROR(<replaceable>msg</>)</literal> and
+ <literal>raise plpy.FATAL(<replaceable>msg</>)</literal> are
+ equivalent to calling
<function>plpy.error</function> and
<function>plpy.fatal</function>, respectively.
+ The other functions only generate messages of different
+ priority levels.
+ Whether messages of a particular priority are reported to the client,
+ written to the server log, or both is controlled by the
+ <xref linkend="guc-log-min-messages"> and
+ <xref linkend="guc-client-min-messages"> configuration
+ variables. See <xref linkend="runtime-config"> for more information.
</para>
<para>
<!--
-$PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.32 2004/11/21 21:17:02 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.33 2004/12/30 21:45:37 tgl Exp $
-->
<chapter id="pltcl">
<para>
PL/Tcl is a loadable procedural language for the
<productname>PostgreSQL</productname> database system
- that enables the Tcl language to be used to write functions and
+ that enables the <ulink url="http://www.tcl.tk/">Tcl</ulink>
+ language to be used to write functions and
trigger procedures.
</para>
The shared object for the <application>PL/Tcl</> and <application>PL/TclU</> call handlers is
automatically built and installed in the
<productname>PostgreSQL</productname>
- library directory if Tcl/Tk support is specified
+ library directory if Tcl support is specified
in the configuration step of the installation procedure. To install
<application>PL/Tcl</> and/or <application>PL/TclU</> in a particular database, use the
<command>createlang</command> program, for example
To create a function in the <application>PL/Tcl</> language, use the standard syntax:
<programlisting>
-CREATE FUNCTION <replaceable>funcname</replaceable>
-(<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$
+CREATE FUNCTION <replaceable>funcname</replaceable> (<replaceable>argument-types</replaceable>) RETURNS <replaceable>return-type</replaceable> AS $$
# PL/Tcl function body
$$ LANGUAGE pltcl;
</programlisting>
<para>
There is currently no support for returning a composite-type
- result value.
+ result value, nor for returning sets.
+ </para>
+
+ <para>
+ <application>PL/Tcl</> does not currently have full support for
+ domain types: it treats a domain the same as the underlying scalar
+ type. This means that constraints associated with the domain will
+ not be enforced. This is not an issue for function arguments, but
+ it is a hazard if you declare a <application>PL/Tcl</> function
+ as returning a domain type.
</para>
</sect1>
<para>
The argument values supplied to a PL/Tcl function's code are simply
the input arguments converted to text form (just as if they had been
- displayed by a <command>SELECT</> statement). Conversely, the <literal>return</>
+ displayed by a <command>SELECT</> statement). Conversely, the
+ <literal>return</>
command will accept any string that is acceptable input format for
- the function's declared return type. So, the PL/Tcl programmer can
- manipulate data values as if they were just text.
+ the function's declared return type. So, within the PL/Tcl function,
+ all values are just text strings.
</para>
</sect1>
command. The global name of this variable is the function's internal
name, and the local name is <literal>GD</>. It is recommended that
<literal>GD</> be used
- for private data of a function. Use regular Tcl global variables
- only for values that you specifically intend to be shared among multiple
- functions.
+ for persistent private data of a function. Use regular Tcl global
+ variables only for values that you specifically intend to be shared among
+ multiple functions.
</para>
<para>
<term><literal><function>spi_exec</function> <optional role="tcl">-count <replaceable>n</replaceable></optional> <optional role="tcl">-array <replaceable>name</replaceable></optional> <replaceable>command</replaceable> <optional role="tcl"><replaceable>loop-body</replaceable></optional></literal></term>
<listitem>
<para>
- Executes an SQL command given as a string. An error in the command
- causes an error to be raised. Otherwise, the return value of <function>spi_exec</function>
- is the number of rows processed (selected, inserted, updated, or
- deleted) by the command, or zero if the command is a utility
- statement. In addition, if the command is a <command>SELECT</> statement, the
- values of the selected columns are placed in Tcl variables as
- described below.
+ Executes an SQL command given as a string. An error in the command
+ causes an error to be raised. Otherwise, the return value of <function>spi_exec</function>
+ is the number of rows processed (selected, inserted, updated, or
+ deleted) by the command, or zero if the command is a utility
+ statement. In addition, if the command is a <command>SELECT</> statement, the
+ values of the selected columns are placed in Tcl variables as
+ described below.
</para>
<para>
- The optional <literal>-count</> value tells
- <function>spi_exec</function> the maximum number of rows
- to process in the command. The effect of this is comparable to
- setting up a query as a cursor and then saying <literal>FETCH <replaceable>n</></>.
+ The optional <literal>-count</> value tells
+ <function>spi_exec</function> the maximum number of rows
+ to process in the command. The effect of this is comparable to
+ setting up a query as a cursor and then saying <literal>FETCH <replaceable>n</></>.
</para>
<para>
- If the command is a <command>SELECT</> statement, the values of the
- result columns are placed into Tcl variables named after the columns.
+ If the command is a <command>SELECT</> statement, the values of the
+ result columns are placed into Tcl variables named after the columns.
If the <literal>-array</> option is given, the column values are
- instead stored into the named associative array, with the
- column names used as array indexes.
+ instead stored into the named associative array, with the
+ column names used as array indexes.
</para>
<para>
If the command is a <command>SELECT</> statement and no <replaceable>loop-body</>
- script is given, then only the first row of results are stored into
- Tcl variables; remaining rows, if any, are ignored. No storing occurs
- if the
- query returns no rows. (This case can be detected by checking the
- result of <function>spi_exec</function>.) For example,
+ script is given, then only the first row of results are stored into
+ Tcl variables; remaining rows, if any, are ignored. No storing occurs
+ if the
+ query returns no rows. (This case can be detected by checking the
+ result of <function>spi_exec</function>.) For example,
<programlisting>
spi_exec "SELECT count(*) AS cnt FROM pg_proc"
</programlisting>
- will set the Tcl variable <literal>$cnt</> to the number of rows in
- the <structname>pg_proc</> system catalog.
+ will set the Tcl variable <literal>$cnt</> to the number of rows in
+ the <structname>pg_proc</> system catalog.
</para>
<para>
If the optional <replaceable>loop-body</> argument is given, it is
- a piece of Tcl script that is executed once for each row in the
- query result. (<replaceable>loop-body</> is ignored if the given
- command is not a <command>SELECT</>.) The values of the current row's columns
- are stored into Tcl variables before each iteration. For example,
+ a piece of Tcl script that is executed once for each row in the
+ query result. (<replaceable>loop-body</> is ignored if the given
+ command is not a <command>SELECT</>.) The values of the current row's columns
+ are stored into Tcl variables before each iteration. For example,
<programlisting>
spi_exec -array C "SELECT * FROM pg_class" {
}
</programlisting>
- will print a log message for every row of <literal>pg_class</>. This
- feature works similarly to other Tcl looping constructs; in
- particular <literal>continue</> and <literal>break</> work in the
- usual way inside the loop body.
+ will print a log message for every row of <literal>pg_class</>. This
+ feature works similarly to other Tcl looping constructs; in
+ particular <literal>continue</> and <literal>break</> work in the
+ usual way inside the loop body.
</para>
<para>
If a column of a query result is null, the target
- variable for it is <quote>unset</> rather than being set.
+ variable for it is <quote>unset</> rather than being set.
</para>
</listitem>
</varlistentry>
<term><function>spi_prepare</function> <replaceable>query</replaceable> <replaceable>typelist</replaceable></term>
<listitem>
<para>
- Prepares and saves a query plan for later execution. The
- saved plan will be retained for the life of the current
- session.<indexterm><primary>preparing a query</><secondary>in
- PL/Tcl</></>
+ Prepares and saves a query plan for later execution. The
+ saved plan will be retained for the life of the current
+
session.<indexterm><primary>preparing a query</><secondary>in
+ PL/Tcl</></>
</para>
<para>
The query may use parameters, that is, placeholders for
- values to be supplied whenever the plan is actually executed.
- In the query string, refer to parameters
- by the symbols <literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal>.
- If the query uses parameters, the names of the parameter types
- must be given as a Tcl list. (Write an empty list for
- <replaceable>typelist</replaceable> if no parameters are used.)
- Presently, the parameter types must be identified by the internal
- type names shown in the system table <literal>pg_type</>; for example <literal>int4</> not
- <literal>integer</>.
+ values to be supplied whenever the plan is actually executed.
+ In the query string, refer to parameters
+ by the symbols <literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal>.
+ If the query uses parameters, the names of the parameter types
+ must be given as a Tcl list. (Write an empty list for
+ <replaceable>typelist</replaceable> if no parameters are used.)
+ Presently, the parameter types must be identified by the internal
+ type names shown in the system table <literal>pg_type</>; for example <literal>int4</> not
+ <literal>integer</>.
</para>
<para>
The return value from <function>spi_prepare</function> is a query ID
- to be used in subsequent calls to <function>spi_execp</function>. See
- <function>spi_execp</function> for an example.
+ to be used in subsequent calls to <function>spi_execp</function>. See
+ <function>spi_execp</function> for an example.
</para>
</listitem>
</varlistentry>
<term><literal><function>spi_execp</> <optional role="tcl">-count <replaceable>n</replaceable></optional> <optional role="tcl">-array <replaceable>name</replaceable></optional> <optional role="tcl">-nulls <replaceable>string</replaceable></optional> <replaceable>queryid</replaceable> <optional role="tcl"><replaceable>value-list</replaceable></optional> <optional role="tcl"><replaceable>loop-body</replaceable></optional></literal></term>
<listitem>
<para>
- Executes a query previously prepared with <function>spi_prepare</>.
- <replaceable>queryid</replaceable> is the ID returned by
- <function>spi_prepare</>. If the query references parameters,
- a <replaceable>value-list</replaceable> must be supplied. This
- is a Tcl list of actual values for the parameters. The list must be
- the same length as the parameter type list previously given to
- <function>spi_prepare</>. Omit <replaceable>value-list</replaceable>
- if the query has no parameters.
+ Executes a query previously prepared with <function>spi_prepare</>.
+ <replaceable>queryid</replaceable> is the ID returned by
+ <function>spi_prepare</>. If the query references parameters,
+ a <replaceable>value-list</replaceable> must be supplied. This
+ is a Tcl list of actual values for the parameters. The list must be
+ the same length as the parameter type list previously given to
+ <function>spi_prepare</>. Omit <replaceable>value-list</replaceable>
+ if the query has no parameters.
</para>
<para>
- The optional value for <literal>-nulls</> is a string of spaces and
- <literal>'n'</> characters telling <function>spi_execp</function>
- which of the parameters are null values. If given, it must have exactly the
- same length as the <replaceable>value-list</replaceable>. If it
- is not given, all the parameter values are nonnull.
+ The optional value for <literal>-nulls</> is a string of spaces and
+ <literal>'n'</> characters telling <function>spi_execp</function>
+ which of the parameters are null values. If given, it must have exactly the
+ same length as the <replaceable>value-list</replaceable>. If it
+ is not given, all the parameter values are nonnull.
</para>
<para>
Except for the way in which the query and its parameters are specified,
- <function>spi_execp</> works just like <function>spi_exec</>.
+ <function>spi_execp</> works just like <function>spi_exec</>.
The <literal>-count</>, <literal>-array</>, and
- <replaceable>loop-body</replaceable> options are the same,
- and so is the result value.
+ <replaceable>loop-body</replaceable> options are the same,
+ and so is the result value.
</para>
<para>
- Here's an example of a PL/Tcl function using a prepared plan:
+ Here's an example of a PL/Tcl function using a prepared plan:
<programlisting>
CREATE FUNCTION t1_count(integer, integer) RETURNS integer AS $$
<term><function>spi_lastoid</></term>
<listitem>
<para>
- Returns the OID of the row inserted by the last
- <function>spi_exec</> or <function>spi_execp</>,
- if the command was a single-row <command>INSERT</>. (If not, you get zero.)
+ Returns the OID of the row inserted by the last
+ <function>spi_exec</> or <function>spi_execp</>,
+ if the command was a single-row <command>INSERT</>. (If not, you get zero.)
</para>
</listitem>
</varlistentry>
<term><function>quote</> <replaceable>string</replaceable></term>
<listitem>
<para>
- Doubles all occurrences of single quote and backslash characters
- in the given string. This may be used to safely quote strings
- that are to be inserted into SQL commands given
- to <function>spi_exec</function> or
- <function>spi_prepare</function>.
- For example, think about an SQL command string like
+ Doubles all occurrences of single quote and backslash characters
+ in the given string. This may be used to safely quote strings
+ that are to be inserted into SQL commands given
+ to <function>spi_exec</function> or
+ <function>spi_prepare</function>.
+ For example, think about an SQL command string like
<programlisting>
"SELECT '$val' AS ret"
</programlisting>
- where the Tcl variable <literal>val</> actually contains
- <literal>doesn't</literal>. This would result
- in the final command string
+ where the Tcl variable <literal>val</> actually contains
+ <literal>doesn't</literal>. This would result
+ in the final command string
<programlisting>
SELECT 'doesn't' AS ret
</programlisting>
- which would cause a parse error during
- <function>spi_exec</function> or
- <function>spi_prepare</function>.
- To work properly, the submitted command should contain
+ which would cause a parse error during
+ <function>spi_exec</function> or
+ <function>spi_prepare</function>.
+ To work properly, the submitted command should contain
<programlisting>
SELECT 'doesn''t' AS ret
</programlisting>
- which can be formed in PL/Tcl using
+ which can be formed in PL/Tcl using
<programlisting>
"SELECT '[ quote $val ]' AS ret"
</programlisting>
One advantage of <function>spi_execp</function> is that you don't
- have to quote parameter values like this, since the parameters are never
- parsed as part of an SQL command string.
+ have to quote parameter values like this, since the parameters are never
+ parsed as part of an SQL command string.
</para>
</listitem>
</varlistentry>
Emits a log or error message. Possible levels are
<literal>DEBUG</>, <literal>LOG</>, <literal>INFO</>,
<literal>NOTICE</>, <literal>WARNING</>, <literal>ERROR</>, and
- <literal>FATAL</>. Most simply emit the given message just like
- the <literal>elog</> C function. <literal>ERROR</>
+ <literal>FATAL</>. <literal>ERROR</>
raises an error condition; if this is not trapped by the surrounding
Tcl code, the error propagates out to the calling query, causing
the current transaction or subtransaction to be aborted. This
<literal>FATAL</> aborts the transaction and causes the current
session to shut down. (There is probably no good reason to use
this error level in PL/Tcl functions, but it's provided for
- completeness.)
+ completeness.) The other levels only generate messages of different
+ priority levels.
+ Whether messages of a particular priority are reported to the client,
+ written to the server log, or both is controlled by the
+ <xref linkend="guc-log-min-messages"> and
+ <xref linkend="guc-client-min-messages"> configuration
+ variables. See <xref linkend="runtime-config"> for more
+ information.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_name</varname></term>
<listitem>
- <para>
- The name of the trigger from the <command>CREATE TRIGGER</command> statement.
- </para>
+ The name of the trigger from the <command>CREATE TRIGGER</command> statement.
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_relid</varname></term>
<listitem>
- <para>
- The object ID of the table that caused the trigger procedure
- to be invoked.
- </para>
+ The object ID of the table that caused the trigger procedure
+ to be invoked.
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_relatts</varname></term>
<listitem>
- <para>
- A Tcl list of the table column names, prefixed with an empty list
+ A Tcl list of the table column names, prefixed with an empty list
element. So looking up a column name in the list with <application>Tcl</>'s
<function>lsearch</> command returns the element's number starting
- with 1 for the first column, the same way the columns are customarily
- numbered in <productname>PostgreSQL</productname>. (Empty list
- elements also appear in the positions of columns that have been
- dropped, so that the attribute numbering is correct for columns
- to their right.)
- </para>
+ with 1 for the first column, the same way the columns are customarily
+
numbered in <productname>PostgreSQL</productname>. (Empty list
+ elements also appear in the positions of columns that have been
+ dropped, so that the attribute numbering is correct for columns
+ to their right.)
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_when</varname></term>
<listitem>
- <para>
- The string <literal>BEFORE</> or <literal>AFTER</> depending on the
- type of trigger call.
- </para>
+ The string <literal>BEFORE</> or <literal>AFTER</> depending on the
+ type of trigger call.
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_level</varname></term>
<listitem>
- <para>
- The string <literal>ROW</> or <literal>STATEMENT</> depending on the
- type of trigger call.
- </para>
+ The string <literal>ROW</> or <literal>STATEMENT</> depending on the
+ type of trigger call.
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$TG_op</varname></term>
<listitem>
- <para>
- The string <literal>INSERT</>, <literal>UPDATE</>, or
- <literal>DELETE</> depending on the type of trigger call.
- </para>
+ The string <literal>INSERT</>, <literal>UPDATE</>, or
+ <literal>DELETE</> depending on the type of trigger call.
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$NEW</varname></term>
<listitem>
- <para>
- An associative array containing the values of the new table
- row for <command>INSERT</> or <command>UPDATE</> actions, or
- empty for <command>DELETE</>. The array is indexed by column
- name. Columns that are null will not appear in the array.
- </para>
+ An associative array containing the values of the new table
+ row for <command>INSERT</> or <command>UPDATE</> actions, or
+ empty for <command>DELETE</>. The array is indexed by column
+ name. Columns that are null will not appear in the array.
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$OLD</varname></term>
<listitem>
- <para>
- An associative array containing the values of the old table
- row for <command>UPDATE</> or <command>DELETE</> actions, or
- empty for <command>INSERT</>. The array is indexed by column
- name. Columns that are null will not appear in the array.
- </para>
+ An associative array containing the values of the old table
+ row for <command>UPDATE</> or <command>DELETE</> actions, or
+ empty for <command>INSERT</>. The array is indexed by column
+ name. Columns that are null will not appear in the array.
+ </para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>$args</varname></term>
<listitem>
- <para>
- A Tcl list of the arguments to the procedure as given in the
- <command>CREATE TRIGGER</command> statement. These arguments are also accessible as
- <literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal> in the procedure body.
- </para>
+ A Tcl list of the arguments to the procedure as given in the
+ <command>CREATE TRIGGER</command> statement. These arguments are also accessible as
+ <literal>$1</literal> ... <literal>$<replaceable>n</replaceable></literal> in the procedure body.
+ </para>
</listitem>
</varlistentry>
<sect1 id="pltcl-unknown">
<title>Modules and the <function>unknown</> command</title>
<para>
- PL/Tcl has support for autoloading Tcl code when used.
- It recognizes a special table, <literal>pltcl_modules</>, which
- is presumed to contain modules of Tcl code. If this table
- exists, the module <literal>unknown</> is fetched from the table
- and loaded into the Tcl interpreter immediately after creating
- the interpreter.
+ PL/Tcl has support for autoloading Tcl code when used.
+ It recognizes a special table, <literal>pltcl_modules</>, which
+ is presumed to contain modules of Tcl code. If this table
+ exists, the module <literal>unknown</> is fetched from the table
+ and loaded into the Tcl interpreter immediately after creating
+ the interpreter.
</para>
<para>
While the <literal>unknown</> module could actually contain any
- initialization script you need, it normally defines a Tcl
- <function>unknown</> procedure that is invoked whenever Tcl does
- not recognize an invoked procedure name. <application>PL/Tcl</>'s standard version
- of this procedure tries to find a module in <literal>pltcl_modules</>
- that will define the required procedure. If one is found, it is
- loaded into the interpreter, and then execution is allowed to
- proceed with the originally attempted procedure call. A
- secondary table <literal>pltcl_modfuncs</> provides an index of
- which functions are defined by which modules, so that the lookup
- is reasonably quick.
+ initialization script you need, it normally defines a Tcl
+ <function>unknown</> procedure that is invoked whenever Tcl does
+
not recognize an invoked procedure name. <application>PL/Tcl</>'s standard version
+ of this procedure tries to find a module in <literal>pltcl_modules</>
+ that will define the required procedure. If one is found, it is
+ loaded into the interpreter, and then execution is allowed to
+ proceed with the originally attempted procedure call. A
+ secondary table <literal>pltcl_modfuncs</> provides an index of
+ which functions are defined by which modules, so that the lookup
+ is reasonably quick.
</para>
<para>
The <productname>PostgreSQL</productname> distribution includes
- support scripts to maintain these tables:
- <command>pltcl_loadmod</>, <command>pltcl_listmod</>,
- <command>pltcl_delmod</>, as well as source for the standard
- <literal>unknown</> module in <filename>share/unknown.pltcl</>. This module
- must be loaded
- into each database initially to support the autoloading mechanism.
+ support scripts to maintain these tables:
+ <command>pltcl_loadmod</>, <command>pltcl_listmod</>,
+ <command>pltcl_delmod</>, as well as source for the standard
+ <literal>unknown</> module in <filename>share/unknown.pltcl</>. This module
+ must be loaded
+ into each database initially to support the autoloading mechanism.
</para>
<para>
The tables <literal>pltcl_modules</> and <literal>pltcl_modfuncs</>
- must be readable by all, but it is wise to make them owned and
- writable only by the database administrator.
+ must be readable by all, but it is wise to make them owned and
+ writable only by the database administrator.
</para>
</sect1>
<!--
-$PostgreSQL: pgsql/doc/src/sgml/spi.sgml,v 1.36 2004/12/13 18:05:09 petere Exp $
+$PostgreSQL: pgsql/doc/src/sgml/spi.sgml,v 1.37 2004/12/30 21:45:37 tgl Exp $
-->
<chapter id="spi">
<note>
<para>
The available procedural languages provide various means to
- execute SQL commands from procedures. Some of these are based on or
- modelled after SPI, so this documentation might be of use for users
+ execute SQL commands from procedures. Most of these facilities are
+ based on SPI, so this documentation might be of use for users
of those languages as well.
</para>
</note>
</para>
<para>
- Note that if during the execution of a procedure the transaction is
- aborted because of an error in a command, then control will not be
- returned to your procedure. Rather, all work will be rolled back
- and the server will wait for the next command from the client. A
- related restriction is the inability to execute
- <command>BEGIN</command>, <command>COMMIT</command>, and
- <command>ROLLBACK</command> (transaction control statements) inside
- a procedure. Both of these restrictions will probably be changed in
- the future.
+ Note that if a command invoked via SPI fails, then control will not be
+ returned to your procedure. Rather, the
+ transaction or subtransaction in which your procedure executes will be
+ rolled back. (This may seem surprising given that the SPI functions mostly
+ have documented error-return conventions. Those conventions only apply
+ for errors detected within the SPI functions themselves, however.)
+ It is possible to recover control after an error by establishing your own
+ subtransaction surrounding SPI calls that might fail. This is not currently
+ documented because the mechanisms required are still in flux.
</para>
<para>
<acronym>SPI</acronym>, directly nested calls to
<function>SPI_connect</function> and
<function>SPI_finish</function> are forbidden.
+ (But see <function>SPI_push</function> and <function>SPI_pop</function>.)
</para>
</refsect1>
<refnamediv>
<refname>SPI_push</refname>
- <refpurpose>pushes SPI stack to allow recursive SPI usage</refpurpose>
+ <refpurpose>push SPI stack to allow recursive SPI usage</refpurpose>
</refnamediv>
<indexterm><primary>SPI_push</primary></indexterm>
<refnamediv>
<refname>SPI_pop</refname>
- <refpurpose>pops SPI stack to return from recursive SPI usage</refpurpose>
+ <refpurpose>pop SPI stack to return from recursive SPI usage</refpurpose>
</refnamediv>
<indexterm><primary>SPI_pop</primary></indexterm>
</para>
<para>
- You may pass multiple commands in one string, and the commands may
- be rewritten by rules. <function>SPI_execute</function> returns the
+ You may pass multiple commands in one string.
+ <function>SPI_execute</function> returns the
result for the command executed last. The <parameter>count</parameter>
limit applies to each command separately, but it is not applied to
hidden commands generated by rules.
<para>
The plan returned by <function>SPI_prepare</function> can be used
- only in the current invocation of the procedure since
+ only in the current invocation of the procedure, since
<function>SPI_finish</function> frees memory allocated for a plan.
But a plan can be saved for longer using the function
<function>SPI_saveplan</function>.
<refnamediv>
<refname>SPI_getargcount</refname>
- <refpurpose>returns the number of arguments needed by a plan
+ <refpurpose>return the number of arguments needed by a plan
prepared by <function>SPI_prepare</function></refpurpose>
</refnamediv>
<refnamediv>
<refname>SPI_getargtypeid</refname>
- <refpurpose>returns the expected <parameter>typeid</parameter> for the specified argument of
+ <refpurpose>return the data type OID for an argument of
a plan prepared by <function>SPI_prepare</function></refpurpose>
</refnamediv>
<refnamediv>
<refname>SPI_is_cursor_plan</refname>
- <refpurpose>returns <symbol>true</symbol> if a plan
+ <refpurpose>return <symbol>true</symbol> if a plan
prepared by <function>SPI_prepare</function> can be used with
<function>SPI_cursor_open</function></refpurpose>
</refnamediv>
<refnamediv>
<refname>SPI_execute_plan</refname>
- <refpurpose>executes a plan prepared by <function>SPI_prepare</function></refpurpose>
+ <refpurpose>execute a plan prepared by <function>SPI_prepare</function></refpurpose>
</refnamediv>
<indexterm><primary>SPI_execute_plan</primary></indexterm>
<refnamediv>
<refname>SPI_execp</refname>
- <refpurpose>executes a plan in read/write mode</refpurpose>
+ <refpurpose>execute a plan in read/write mode</refpurpose>
</refnamediv>
<indexterm><primary>SPI_execp</primary></indexterm>
<title>Description</title>
<para>
- <function>SPI_fname</function> returns the column name of the
+ <function>SPI_fname</function> returns a copy of the column name of the
specified column. (You can use <function>pfree</function> to
release the copy of the name when you don't need it anymore.)
</para>
<title>Description</title>
<para>
- <function>SPI_gettype</function> returns the data type name of the
+ <function>SPI_gettype</function> returns a copy of the data type name of the
specified column. (You can use <function>pfree</function> to
release the copy of the name when you don't need it anymore.)
</para>
<title>Description</title>
<para>
- <function>SPI_getrelname</function> returns the name of the
+ <function>SPI_getrelname</function> returns a copy of the name of the
specified relation. (You can use <function>pfree</function> to
release the copy of the name when you don't need it anymore.)
</para>
object. <function>SPI_palloc</function> allocates memory in the
<quote>upper executor context</quote>, that is, the memory context
that was current when <function>SPI_connect</function> was called,
- which is precisely the right context for return a value from your
+ which is precisely the right context for a value returned from your
procedure.
</para>
<listitem>
<para>
array of the numbers of the columns that are to be changed
- (count starts at 1)
+ (column numbers start at 1)
</para>
</listitem>
</varlistentry>
<refnamediv>
<refname>SPI_freetuple</refname>
- <refpurpose>frees a row allocated in the upper executor context</refpurpose>
+ <refpurpose>free a row allocated in the upper executor context</refpurpose>
</refnamediv>
<indexterm><primary>SPI_freetuple</primary></indexterm>
<title>Visibility of Data Changes</title>
<para>
- The following two rules govern the visibility of data changes in
+ The following rules govern the visibility of data changes in
functions that use SPI (or any other C function):
<itemizedlist>
<listitem>
<para>
During the execution of an SQL command, any data changes made by
- the command (or by function called by the command, including
- trigger functions) are invisible to the command. For
- example, in command
+ the command are invisible to the command itself. For
+ example, in
<programlisting>
INSERT INTO a SELECT * FROM a;
</programlisting>
(during the execution of C) or after C is done.
</para>
</listitem>
+
+ <listitem>
+ <para>
+ Commands executed via SPI inside a function called by an SQL command
+ (either an ordinary function or a trigger) follow one or the
+ other of the above rules depending on the read/write flag passed
+ to SPI. Commands executed in read-only mode follow the first
+ rule: they can't see changes of the calling command. Commands executed
+ in read-write mode follow the second rule: they can see all changes made
+ so far.
+ </para>
+ </listitem>
+
+ <listitem>
+ <para>
+ All standard procedural languages set the SPI read-write mode
+ depending on the volatility attribute of the function. Commands of
+ <literal>STABLE</> and <literal>IMMUTABLE</> functions are done in
+ read-only mode, while commands of <literal>VOLATILE</> functions are
+ done in read-write mode. While authors of C functions are able to
+ violate this convention, it's unlikely to be a good idea to do so.
+ </para>
+ </listitem>
</itemizedlist>
</para>
<para>
(This function uses call convention version 0, to make the example
- easier to understand. In real applications you should user the new
+ easier to understand. In real applications you should use the new
version 1 interface.)
</para>
<!--
-$PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.91 2004/12/30 03:13:56 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/xfunc.sgml,v 1.92 2004/12/30 21:45:37 tgl Exp $
-->
<sect1 id="xfunc">
<title>Procedural Language Functions</title>
<para>
+ <productname>PostgreSQL</productname> allows user-defined functions
+ to be written in other languages besides SQL and C. These other
+ languages are generically called <firstterm>procedural
+ languages</firstterm> (<acronym>PL</>s).
Procedural languages aren't built into the
<productname>PostgreSQL</productname> server; they are offered
- by loadable modules. Please refer to the documentation of the
- procedural language in question for details about the syntax and how the
- function body is interpreted for each language.
- </para>
-
- <para>
- There are currently four procedural languages available in the
- standard <productname>PostgreSQL</productname> distribution:
- <application>PL/pgSQL</application>, <application>PL/Tcl</application>,
- <application>PL/Perl</application>, and
- <application>PL/Python</application>.
- Refer to <xref linkend="xplang"> for more information.
- Other languages can be defined by users.
- The basics of developing a new procedural language are covered in <xref
- linkend="plhandler">.
+ by loadable modules.
+ See <xref linkend="xplang"> and following chapters for more
+ information.
</para>
</sect1>
<!--
-$PostgreSQL: pgsql/doc/src/sgml/xplang.sgml,v 1.27 2004/12/30 03:13:56 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/xplang.sgml,v 1.28 2004/12/30 21:45:37 tgl Exp $
-->
<chapter id="xplang">
</indexterm>
<para>
- <productname>PostgreSQL</productname> allows users to add new
- programming languages to be available for writing functions and
- procedures. These are called <firstterm>procedural
- languages</firstterm> (PL). In the case of a function or trigger
- procedure written in a procedural language, the database server has
+ <productname>PostgreSQL</productname> allows user-defined functions
+ to be written in other languages besides SQL and C. These other
+ languages are generically called <firstterm>procedural
+ languages</firstterm> (<acronym>PL</>s). For a function
+ written in a procedural language, the database server has
no built-in knowledge about how to interpret the function's source
text. Instead, the task is passed to a special handler that knows
the details of the language. The handler could either do all the
work of parsing, syntax analysis, execution, etc. itself, or it
could serve as <quote>glue</quote> between
<productname>PostgreSQL</productname> and an existing implementation
- of a programming language. The handler itself is a special
+ of a programming language. The handler itself is a
C language function compiled into a shared object and
- loaded on demand.
+ loaded on demand, just like any other C function.
</para>
<para>
- Writing a handler for a new procedural language is described in
- <xref linkend="plhandler">. Several procedural languages are
- available in the core <productname>PostgreSQL</productname>
- distribution, which can serve as examples.
+ There are currently four procedural languages available in the
+ standard <productname>PostgreSQL</productname> distribution:
+ <application>PL/pgSQL</application> (<xref linkend="plpgsql">),
+ <application>PL/Tcl</application> (<xref linkend="pltcl">),
+ <application>PL/Perl</application> (<xref linkend="plperl">), and
+ <application>PL/Python</application> (<xref linkend="plpython">).
+ Other languages can be defined by users.
+ The basics of developing a new procedural language are covered in <xref
+ linkend="plhandler">.
</para>
<para>
A procedural language must be <quote>installed</quote> into each
database where it is to be used. But procedural languages installed in
the database <literal>template1</> are automatically available in all
- subsequently created databases. So the database administrator can
+ subsequently created databases, since their entries in
+ <literal>template1</> will be copied by <command>CREATE DATABASE</>.
+ So the database administrator can
decide which languages are available in which databases and can make
some languages available by default if he chooses.
</para>
<para>
For the languages supplied with the standard distribution, the
- program <command>createlang</command> may be used to install the
+ program <xref linkend="app-createlang"> may be used to install the
language instead of carrying out the details by hand. For
example, to install the language
<application>PL/pgSQL</application> into the database
</title>
<para>
- A procedural language is installed in a database in three steps,
+ A procedural language is installed in a database in four steps,
which must be carried out by a database superuser. The
- <command>createlang</command> program automates <xref
- linkend="xplang-install-cr1"> and <xref
- linkend="xplang-install-cr2">.
+ <command>createlang</command> program automates all but <xref
+ linkend="xplang-install-cr1">.
</para>
- <step performance="required">
+ <step performance="required" id="xplang-install-cr1">
<para>
The shared object for the language handler must be compiled and
installed into an appropriate library directory. This works in the same
way as building and installing modules with regular user-defined C
- functions does; see <xref linkend="dfunc">.
+ functions does; see <xref linkend="dfunc">. Often, the language
+ handler will depend on an external library that provides the actual
+ programming language engine; if so, that must be installed as well.
</para>
</step>
- <step performance="required" id="xplang-install-cr1">
+ <step performance="required" id="xplang-install-cr2">
<para>
The handler must be declared with the command
<synopsis>
</para>
</step>
- <step performance="required" id="xplang-install-cr2">
+ <step performance="optional" id="xplang-install-cr3">
+ <para>
+ Optionally, the language handler may provide a <quote>validator</>
+ function that checks a function definition for correctness without
+ actually executing it. The validator function is called by
+ <command>CREATE FUNCTION</> if it exists. If a validator function
+ is provided by the handler, declare it with a command like
+<synopsis>
+CREATE FUNCTION <replaceable>validator_function_name</replaceable>(oid)
+ RETURNS void
+ AS '<replaceable>path-to-shared-object</replaceable>'
+ LANGUAGE C;
+</synopsis>
+ </para>
+ </step>
+
+ <step performance="required" id="xplang-install-cr4">
<para>
The PL must be declared with the command
<synopsis>
CREATE <optional>TRUSTED</optional> <optional>PROCEDURAL</optional> LANGUAGE <replaceable>language-name</replaceable>
- HANDLER <replaceable>handler_function_name</replaceable>;
+ HANDLER <replaceable>handler_function_name</replaceable>
+ <optional>VALIDATOR <replaceable>validator_function_name</replaceable></optional> ;
</synopsis>
The optional key word <literal>TRUSTED</literal> specifies that
ordinary database users that have no superuser privileges should
</para>
<para>
+ <application>PL/pgSQL</application> has a validator function,
+ so we declare that too:
+
+<programlisting>
+CREATE FUNCTION plpgsql_validator(oid) RETURNS void AS
+ '$libdir/plpgsql' LANGUAGE C;
+</programlisting>
+ </para>
+
+ <para>
The command
<programlisting>
CREATE TRUSTED PROCEDURAL LANGUAGE plpgsql
- HANDLER plpgsql_call_handler;
+ HANDLER plpgsql_call_handler
+ VALIDATOR plpgsql_validator;
</programlisting>
- then defines that the previously declared call handler function
+ then defines that the previously declared functions
should be invoked for functions and trigger procedures where the
language attribute is <literal>plpgsql</literal>.
</para>
In a default <productname>PostgreSQL</productname> installation,
the handler for the <application>PL/pgSQL</application> language
is built and installed into the <quote>library</quote>
- directory. If <application>Tcl/Tk</> support is configured in, the handlers for
+ directory. If <application>Tcl</> support is configured in, the handlers for
<application>PL/Tcl</> and <application>PL/TclU</> are also built and installed in the same
location. Likewise, the <application>PL/Perl</> and <application>PL/PerlU</> handlers are built
and installed if Perl support is configured, and <application>PL/PythonU</> is
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