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Reduce formatting entropy

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Peter Eisentraut 2004-11-06 14:32:10 +00:00
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doc/src/sgml/plperl.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.29 2004/10/15 16:51:48 momjian Exp $
$PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.30 2004/11/06 14:32:10 petere Exp $
-->
<chapter id="plperl">
@ -37,7 +37,6 @@ $PostgreSQL: pgsql/doc/src/sgml/plperl.sgml,v 2.29 2004/10/15 16:51:48 momjian E
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>
@ -85,22 +84,19 @@ $$ LANGUAGE plperl;
</para>
<para>
If an SQL <literal>NULL</literal> value<indexterm><primary>null
value</><secondary sortas="PL/Perl">in PL/Perl</></indexterm> is
passed to a function, the argument value will appear as
<quote>undefined</> in Perl. The above function definition will not
behave very nicely with <literal>NULL</literal> inputs (in fact, it
will act as though they are zeroes). We could add <literal>STRICT</>
to the function definition to make
<productname>PostgreSQL</productname> do something more reasonable: if
a <literal>NULL</literal> value is passed, the function will not be
called at all, but will just return a <literal>NULL</literal> result
automatically. Alternatively, we could check for undefined inputs in
the function body. For example, suppose that we wanted
<function>perl_max</function> with one <literal>NULL</literal> and one
non-<literal>NULL</literal> argument to return the
non-<literal>NULL</literal> argument, rather than a
<literal>NULL</literal> value:
If an SQL null value<indexterm><primary>null value</><secondary
sortas="PL/Perl">in PL/Perl</></indexterm> is passed to a function,
the argument value will appear as <quote>undefined</> in Perl. The
above function definition will not behave very nicely with null
inputs (in fact, it will act as though they are zeroes). We could
add <literal>STRICT</> to the function definition to make
<productname>PostgreSQL</productname> do something more reasonable:
if a null value is passed, the function will not be called at all,
but will just return a null result automatically. Alternatively,
we could check for undefined inputs in the function body. For
example, suppose that we wanted <function>perl_max</function> with
one null and one nonnull argument to return the nonnull argument,
rather than a null value:
<programlisting>
CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS $$
@ -114,12 +110,9 @@ CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS $$
return $b;
$$ LANGUAGE plperl;
</programlisting>
</para>
<para>
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.
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.
</para>
<para>
@ -142,26 +135,23 @@ $$ LANGUAGE plperl;
SELECT name, empcomp(employee) FROM employee;
</programlisting>
</para>
<para>
There is now support for returning a composite-type result value.
</para>
</sect1>
<sect1 id="plperl-database">
<title>Database Access from PL/Perl</title>
<para>
Access to the database itself from your Perl function can be done via
spi_exec_query, or via an experimental module <ulink
Access to the database itself from your Perl function can be done
via the function <function>spi_exec_query</function> described
below, 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
(also available at <ulink
url="http://www.cpan.org/SITES.html"><acronym>CPAN</> 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>
<varname>$pg_dbh</varname> that can be used to perform queries with
normal <acronym>DBI</>
syntax.<indexterm><primary>DBI</></indexterm>
</para>
<para>
@ -173,59 +163,56 @@ SELECT name, empcomp(employee) FROM employee;
<primary>spi_exec_query</primary>
<secondary>in PL/Perl</secondary>
</indexterm>
<term><literal><function>spi_exec_query</>(<replaceable>query</replaceable> [, <replaceable>max-rows</replaceable>])</literal></term>
<term><literal><function>spi_exec_query</>(<replaceable>command</replaceable>)</literal></term>
<listitem>
<para>
Executes an SQL command. Here is an example of a query
(<command>SELECT</command> command) 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 the table
<literal>my_table</literal>. If <literal>my_table</literal>
has a column <literal>my_column</literal>, it could be accessed
like this:
<programlisting>
$foo = $rv->{rows}[$i]->{my_column};
</programlisting>
The total number of rows returned can be accessed like this:
<programlisting>
$nrows = @{$rv->{rows}};
</programlisting>
</para>
<para>
Here is an example using a different command type:
<programlisting>
$query = "INSERT INTO my_table VALUES (1, 'test')";
$rv = spi_exec_query($query);
</programlisting>
You can then access the command status (e.g.,
<literal>SPI_OK_INSERT</literal>) like this:
<programlisting>
$res = $rv->{status};
</programlisting>
To get the number of rows affected, do:
<programlisting>
$nrows = $rv->{rows};
</programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
<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>
<term><literal><function>elog</>(<replaceable>level</replaceable>, <replaceable>msg</replaceable>)</literal></term>
<listitem>
<para>
Emit a log or error message. Possible levels are
@ -255,102 +242,94 @@ $nrows = $rv->{rows};
</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. Note that a composite type is always represented as a
hash reference.
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
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');
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 $$
CREATE FUNCTION test_munge() RETURNS SETOF test AS $$
my $res = [];
my $rv = spi_exec_query('select i,v from test;');
my $rv = spi_exec_query('select i, v from test;');
my $status = $rv->{status};
my $rows = @{$rv->{rows}};
my $processed = $rv->{processed};
foreach my $rn (0..$rows-1) {
foreach my $rn (0 .. $rows - 1) {
my $row = $rv->{rows}[$rn];
$row->{i} += 200 if defined($row->{i});
$row->{v} =~ tr/A-Za-z/a-zA-Z/ if (defined($row->{v}));
push @$res,$row;
push @$res, $row;
}
return $res;
$$;
$$ LANGUAGE plperl;
select * from test_munge();
SELECT * FROM test_munge();
</programlisting>
</para>
<para>
Here is an example of a PL/Perl function returning a composite type:
<programlisting>
Here is an example of a PL/Perl function returning a composite
type:
<programlisting>
CREATE TYPE testrowperl AS (f1 integer, f2 text, f3 text);
CREATE OR REPLACE FUNCTION perl_row() RETURNS testrowperl AS $$
return {f2 => 'hello', f1 => 1, f3 => 'world'};
return {f2 => 'hello', f1 => 1, f3 => 'world'};
$$ LANGUAGE plperl;
</programlisting>
</programlisting>
</para>
<para>
Here is an example of a PL/Perl function returning a rowset of a
composite type. As a rowset is always a reference to an array
and a composite type is always a reference to a hash, a rowset of a
composite type is a reference to an array of hash references.
<programlisting>
Here is an example of a PL/Perl function returning a row set of a
composite type. Since a row set is always a reference to an array
and a composite type is always a reference to a hash, a rowset of a
composite type is a reference to an array of hash references.
<programlisting>
CREATE TYPE testsetperl AS (f1 integer, f2 text, f3 text);
CREATE OR REPLACE FUNCTION perl_set() RETURNS SETOF testsetperl AS $$
return[
{f1 => 1, f2 => 'hello', f3 => 'world'},
{f1 => 2, f2 => 'hello', f3 => 'postgres'},
{f1 => 3, f2 => 'hello', f3 => 'plperl'}
];
return [
{ f1 => 1, f2 => 'Hello', f3 => 'World' },
{ f1 => 2, f2 => 'Hello', f3 => 'PostgreSQL' },
{ f1 => 3, f2 => 'Hello', f3 => 'PL/Perl' }
];
$$ LANGUAGE plperl;
</programlisting>
</para>
</sect1>
<sect1 id="plperl-global">
<title>Global Values in PL/Perl</title>
<para>
You can use the %_SHARED to store data between function calls.
</para>
<para>
For example:
You can use the global hash <varname>%_SHARED</varname> to store
data between function calls. For example:
<programlisting>
CREATE OR REPLACE FUNCTION set_var(name TEXT, val TEXT) RETURNS TEXT AS $$
CREATE OR REPLACE FUNCTION set_var(name text, val text) RETURNS text AS $$
if ($_SHARED{$_[0]} = $_[1]) {
return 'ok';
} else {
return "Can't set shared variable $_[0] to $_[1]";
return "can't set shared variable $_[0] to $_[1]";
}
$$ LANGUAGE plperl;
CREATE OR REPLACE FUNCTION get_var(name TEXT) RETURNS text AS $$
CREATE OR REPLACE FUNCTION get_var(name text) RETURNS text AS $$
return $_SHARED{$_[0]};
$$ LANGUAGE plperl;
SELECT set_var('sample', $q$Hello, PL/Perl! How's tricks?$q$);
SELECT set_var('sample', 'Hello, PL/Perl! How's tricks?');
SELECT get_var('sample');
</programlisting>
</para>
</sect1>
<sect1 id="plperl-trusted">
@ -413,63 +392,166 @@ $$ 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>$_TD</varname> hash reference.
</para>
PL/Perl can be used to write trigger functions. The global hash
reference <varname>$_TD</varname> contains information about the
current trigger event. The parts of <varname>$_TD</varname> hash
reference are:
<para>
Some useful parts of the $_TD hash reference are:
<variablelist>
<varlistentry>
<term><literal>$_TD->{new}{foo}</literal></term>
<listitem>
<para>
<literal>NEW</literal> value of column <literal>foo</literal>
</para>
</listitem>
</varlistentry>
<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.
$_TD{argc} # Number of arguments to the trigger. Why is this here?
</programlisting>
<varlistentry>
<term><literal>$_TD->{old}{foo}</literal></term>
<listitem>
<para>
<literal>OLD</literal> value of column <literal>foo</literal>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>$_TD{name}</literal></term>
<listitem>
<para>
Name of the trigger being called
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>$_TD{event}</literal></term>
<listitem>
<para>
Trigger event: <literal>INSERT</>, <literal>UPDATE</>, <literal>DELETE</>, or <literal>UNKNOWN</>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>$_TD{when}</literal></term>
<listitem>
<para>
When the trigger was called: <literal>BEFORE</literal>, <literal>AFTER</literal>, or <literal>UNKNOWN</literal>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>$_TD{level}</literal></term>
<listitem>
<para>
The trigger level: <literal>ROW</literal>, <literal>STATEMENT</literal>, or <literal>UNKNOWN</literal>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>$_TD{relid}</literal></term>
<listitem>
<para>
OID of the table on which the trigger fired
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>$_TD{relname}</literal></term>
<listitem>
<para>
Name of the table on which the trigger fired
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>@{$_TD{argv}}</literal></term>
<listitem>
<para>
Arguments of the trigger function
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>$_TD{argc}</literal></term>
<listitem>
<para>
Number of arguments of the trigger functions
</para>
</listitem>
</varlistentry>
</variablelist>
</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>
<variablelist>
<varlistentry>
<term><literal>return;</literal></term>
<listitem>
<para>
Execute the statement
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>"SKIP"</literal></term>
<listitem>
<para>
Don't execute the statement
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>"MODIFY"</literal></term>
<listitem>
<para>
Indicates that the <literal>NEW</literal> rows was modified by
the trigger function
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
Here is an example of a trigger function, illustrating some of the
above.
Here is an example of a trigger function, illustrating some of the
above:
<programlisting>
CREATE TABLE test (
i int,
v varchar
i int,
v varchar
);
CREATE OR REPLACE FUNCTION valid_id() RETURNS trigger AS $$
if (($_TD->{new}{i}>=100) || ($_TD->{new}{i}<=0)) {
return "SKIP"; # Skip INSERT/UPDATE command
if (($_TD->{new}{i} &gt;= 100) || ($_TD->{new}{i} &lt;= 0)) {
return "SKIP"; # skip INSERT/UPDATE command
} elsif ($_TD->{new}{v} ne "immortal") {
$_TD->{new}{v} .= "(modified by trigger)";
return "MODIFY"; # Modify tuple and proceed INSERT/UPDATE command
return "MODIFY"; # modify row and execute INSERT/UPDATE command
} else {
return; # Proceed INSERT/UPDATE command
return; # execute INSERT/UPDATE command
}
$$ LANGUAGE plperl;
CREATE TRIGGER "test_valid_id_trig" BEFORE INSERT OR UPDATE ON test
FOR EACH ROW EXECUTE PROCEDURE "valid_id"();
CREATE TRIGGER test_valid_id_trig
BEFORE INSERT OR UPDATE ON test
FOR EACH ROW EXECUTE PROCEDURE valid_id();
</programlisting>
</para>
</sect1>
@ -491,19 +573,19 @@ FOR EACH ROW EXECUTE PROCEDURE "valid_id"();
<listitem>
<para>
<application>Full SPI</application> is not yet implemented.
SPI is not yet fully implemented.
</para>
</listitem>
<listitem>
<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>
<listitem>
<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.
</para>
</listitem>
</itemizedlist>
</para>
</sect1>