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Postgres FD Implementation
Commit 8eeae3e1 authored by Bruce Momjian's avatar Bruce Momjian
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Please find enclosed a patch that matches the PL/Perl documentation 

(fairly closely, I hope) to the current PL/Perl implementation.

David Fetter
parent 4690cc9c
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doc/src/sgml/plperl.sgml
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<!--
$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.25 2004/07/21 20:34:43 momjian Exp $
$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.26 2004/07/21 20:44:52 momjian Exp $
-->
<chapter id="plperl">
......@@ -34,9 +34,10 @@ $PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.25 2004/07/21 20:34:43 momjian E
<note>
<para>
Users of source packages must specially enable the build of
PL/Perl during the installation process. (Refer to the installation
instructions for more information.) Users of binary packages
might find PL/Perl in a separate subpackage.
PL/Perl during the installation process. (Refer to <xref
linkend="install-short"> for more information.) Users of
binary packages might find PL/Perl in a separate subpackage.
</para>
</note>
......@@ -54,7 +55,7 @@ $$ LANGUAGE plperl;
The body of the function is ordinary Perl code. Since the body of
the function is treated as a string by
<productname>PostgreSQL</productname>, it can be specified using
dollar quoting (as shown above), or via the usual single quote
dollar quoting (as shown above), or via the legacy single quote
syntax (see <xref linkend="sql-syntax-strings"> for more
information).
</para>
......@@ -79,19 +80,22 @@ $$ LANGUAGE plperl;
</para>
<para>
If an SQL null value<indexterm><primary>null value</><secondary
sortas="PL/Perl">in PL/Perl</></indexterm> is passed to a function,
the argument value will appear as <quote>undefined</> in Perl. The
above function definition will not behave very nicely with null
inputs (in fact, it will act as though they are zeroes). We could
add <literal>STRICT</> to the function definition to make
<productname>PostgreSQL</productname> do something more reasonable:
if a null value is passed, the function will not be called at all,
but will just return a null result automatically. Alternatively,
we could check for undefined inputs in the function body. For
example, suppose that we wanted <function>perl_max</function> with
one null and one non-null argument to return the non-null argument,
rather than a null value:
If an SQL <literal>NULL</literal> value<indexterm><primary>null
value</><secondary sortas="PL/Perl">in PL/Perl</></indexterm> is
passed to a function, the argument value will appear as
<quote>undefined</> in Perl. The above function definition will not
behave very nicely with <literal>NULL</literal> inputs (in fact, it
will act as though they are zeroes). We could add <literal>STRICT</>
to the function definition to make
<productname>PostgreSQL</productname> do something more reasonable: if
a <literal>NULL</literal> value is passed, the function will not be
called at all, but will just return a <literal>NULL</literal> result
automatically. Alternatively, we could check for undefined inputs in
the function body. For example, suppose that we wanted
<function>perl_max</function> with one <literal>NULL</literal> and one
non-<literal>NULL</literal> argument to return the
non-<literal>NULL</literal> argument, rather than a
<literal>NULL</literal> value:
<programlisting>
CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS $$
......@@ -108,9 +112,9 @@ $$ LANGUAGE plperl;
</para>
<para>
As shown above, to return an SQL null value from a PL/Perl
function, return an undefined value. This can be done whether the
function is strict or not.
As shown above, to return an SQL <literal>NULL</literal> value from
a PL/Perl function, return an undefined value. This can be done
whether the function is strict or not.
</para>
<para>
......@@ -127,7 +131,7 @@ CREATE TABLE employee (
CREATE FUNCTION empcomp(employee) RETURNS integer AS $$
my ($emp) = @_;
return $emp->{'basesalary'} + $emp->{'bonus'};
return $emp->{basesalary} + $emp->{bonus};
$$ LANGUAGE plperl;
SELECT name, empcomp(employee) FROM employee;
......@@ -135,35 +139,9 @@ SELECT name, empcomp(employee) FROM employee;
</para>
<para>
There is currently no support for returning a composite-type result
value.
There is now support for returning a composite-type result value.
</para>
<tip>
<para>
Because the function body is passed as an SQL string literal to
<command>CREATE FUNCTION</command>, you have to use dollar quoting
or escape single quotes and backslashes within your Perl source,
typically by doubling them. Another possible approach is to avoid
writing single quotes by using Perl's extended quoting operators
(<literal>q[]</literal>, <literal>qq[]</literal>,
<literal>qw[]</literal>).
</para>
</tip>
</sect1>
<sect1 id="plperl-data">
<title>Data Values in PL/Perl</title>
<para>
The argument values supplied to a PL/Perl function's code are
simply the input arguments converted to text form (just as if they
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>
</sect1>
<sect1 id="plperl-database">
......@@ -171,25 +149,77 @@ SELECT name, empcomp(employee) FROM employee;
<para>
Access to the database itself from your Perl function can be done via
an experimental module <ulink
spi_exec_query, or via an experimental module <ulink
url="http://www.cpan.org/modules/by-module/DBD/APILOS/"><literal>DBD::PgSPI</literal></ulink>
(also available at <ulink url="http://www.cpan.org/SITES.html"><acronym>CPAN</>
mirror sites</ulink>). This module makes available a
mirror sites</ulink>). This module makes available a
<acronym>DBI</>-compliant database-handle named
<varname>$pg_dbh</varname> that can be used to perform queries
with normal <acronym>DBI</> syntax.<indexterm><primary>DBI</></indexterm>
</para>
<para>
PL/Perl itself presently provides only one additional Perl command:
PL/Perl itself presently provides two additional Perl commands:
<variablelist>
<varlistentry>
<indexterm>
<primary>spi_exec_query</primary>
<secondary>in PL/Perl</secondary>
</indexterm>
<indexterm>
<primary>elog</primary>
<secondary>in PL/Perl</secondary>
</indexterm>
<term><function>spi_exec_query(</> [ <replaceable>SELECT query</replaceable> [, <replaceable>max_rows</replaceable>]] | [<replaceable>non-SELECT query</replaceable>] ) </term>
<listitem>
<para>
Here is an example of a SELECT query with the optional maximum
number of rows.
<programlisting>
$rv = spi_exec_query('SELECT * from my_table', 5);
</programlisting>
This returns up to 5 rows from my_table.
</para>
<para>
If my_table has a column my_column, it would be accessed as
<programlisting>
$foo = $rv->{rows}[$i]->{my_column};
</programlisting>
</para>
<para>
The number of rows actually returned would be:
<programlisting>
$nrows = @{$rv->{rows}};
</programlisting>
</para>
<para>
Here is an example using a non-SELECT statement.
<programlisting>
$query = "INSERT INTO my_table VALUES (1, 'test')";
$rv = spi_exec_query($query);
</programlisting>
You can then access status (SPI_OK_INSERT, e.g.) like this.
<programlisting>
$res = $rv->{status};
</programlisting>
</para>
<para>
To get the rows affected, do:
<programlisting>
$nrows = $rv->{rows};
</programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><function>elog</> <replaceable>level</replaceable>, <replaceable>msg</replaceable></term>
<listitem>
<para>
......@@ -206,6 +236,111 @@ SELECT name, empcomp(employee) FROM employee;
</para>
</sect1>
<sect1 id="plperl-data">
<title>Data Values in PL/Perl</title>
<para>
The argument values supplied to a PL/Perl function's code are
simply the input arguments converted to text form (just as if they
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 now return rowsets and composite types, and rowsets of
composite types.
</para>
<para>
Here is an example of a PL/Perl function returning a rowset of a row type:
<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 language plperl as $$
my $res = [];
my $rv = spi_exec_query('select i,v from test;');
my $status = $rv->{status};
my $rows = @{$rv->{rows}};
my $processed = $rv->{processed};
foreach my $rn (0..$rows-1) {
my $row = $rv->{rows}[$rn];
$row->{i} += 200 if defined($row->{i});
$row->{v} =~ tr/A-Za-z/a-zA-Z/ if (defined($row->{v}));
push @$res,$row;
}
return $res;
$$;
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 rowset of a composite type.
<programlisting>
CREATE TYPE testsetperl AS (f1 integer, f2 text, f3 text);
CREATE OR REPLACE FUNCTION perl_set() RETURNS SETOF testsetperl AS $$
return[
{f1 => 1, f2 => 'hello', f3 => 'world'},
{f1 => 2, f2 => 'hello', f3 => 'postgres'},
{f1 => 3, f2 => 'hello', f3 => 'plperl'}
];
$$ LANGUAGE plperl;
</programlisting>
</para>
</sect1>
<sect1 id="plperl-global">
<title>Global Values in PL/Perl</title>
<para>
You can use the %_SHARED to store data between function calls. WHY
IS THIS A HASH, AND NOT A HASH REF?
</para>
<para>
For example:
<programlisting>
CREATE OR REPLACE FUNCTION set_var(TEXT) RETURNS TEXT AS $$
$_SHARED{first} = 'Hello, PL/Perl!';
return 'ok';
$$ LANGUAGE plperl;
CREATE OR REPLACE FUNCTION get_var() RETURNS text AS $$
return $_SHARED{first};
$$ LANGUAGE plperl;
SELECT set_var('hello plperl');
SELECT get_var();
</programlisting>
</para>
</sect1>
<sect1 id="plperl-trusted">
<title>Trusted and Untrusted PL/Perl</title>
......@@ -266,9 +401,69 @@ $$ LANGUAGE plperl;
<literal>plperlu</>, execution would succeed.
</para>
</sect1>
<sect1 id="plperl-triggers">
<title>PL/Perl Triggers</title>
<para>
PL/Perl can now be used to write trigger functions using the
<varname>$_TD</varname> hash reference.
</para>
<para>
Some useful parts of the $_TD hash reference are:
<programlisting>
$_TD->{new}{foo} # NEW value of column foo
$_TD->{old}{bar} # OLD value of column bar
$_TD{name} # Name of the trigger being called
$_TD{event} # INSERT, UPDATE, DELETE or UNKNOWN
$_TD{when} # BEFORE, AFTER or UNKNOWN
$_TD{level} # ROW, STATEMENT or UNKNOWN
$_TD{relid} # Relation ID of the table on which the trigger occurred.
$_TD{relname} # Name of the table on which the trigger occurred.
@{$_TD{argv}} # Array of arguments to the trigger function. May be empty.
$_TD{argc} # Number of arguments to the trigger. Why is this here?
</programlisting>
</para>
<para>
Triggers can return one of the following:
<programlisting>
return; -- Executes the statement
SKIP; -- Doesn't execute the statement
MODIFY; -- Says it modified a NEW row
</programlisting>
</para>
<para>
Here is an example of a trigger function, illustrating some of the
above.
<programlisting>
CREATE TABLE test (
i int,
v varchar
);
CREATE OR REPLACE FUNCTION valid_id() RETURNS trigger AS $$
if (($_TD->{new}{i}>=100) || ($_TD->{new}{i}<=0)) {
return "SKIP"; # Skip INSERT/UPDATE command
} elsif ($_TD->{new}{v} ne "immortal") {
$_TD->{new}{v} .= "(modified by trigger)";
return "MODIFY"; # Modify tuple and proceed INSERT/UPDATE command
} else {
return; # Proceed INSERT/UPDATE command
}
$$ LANGUAGE plperl;
CREATE TRIGGER "test_valid_id_trig" BEFORE INSERT OR UPDATE ON test
FOR EACH ROW EXECUTE PROCEDURE "valid_id"();
</programlisting>
</para>
</sect1>
<sect1 id="plperl-missing">
<title>Missing Features</title>
<title>Limitations and Missing Features</title>
<para>
The following features are currently missing from PL/Perl, but they
......@@ -278,26 +473,25 @@ $$ LANGUAGE plperl;
<listitem>
<para>
PL/Perl functions cannot call each other directly (because they
are anonymous subroutines inside Perl). There's presently no
way for them to share global variables, either.
are anonymous subroutines inside Perl).
</para>
</listitem>
<listitem>
<para>
PL/Perl cannot be used to write trigger
functions.<indexterm><primary>trigger</><secondary>in
PL/Perl</></indexterm>
<application>Full SPI</application> is not yet implemented.
</para>
</listitem>
<listitem>
<para>
<application>DBD::PgSPI</applicatioN> or similar capability
should be integrated into the standard
<productname>PostgreSQL</productname> distribution.
</para>
<para>
In the current implementation, if you are fetching or
returning very large datasets, 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.
</para>
</listitem>
</itemizedlist>
</para>
</sect1>
......
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