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><H1
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><A
NAME="PLPERL-BUILTINS"
>41.3. Built-in Functions</A
></H1
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="PLPERL-DATABASE"
>41.3.1. Database Access from PL/Perl</A
></H2
><P
>   Access to the database itself from your Perl function can be done
   via the following functions:
  </P
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>spi_exec_query</CODE
>(<TT
CLASS="REPLACEABLE"
><I
>query</I
></TT
> [, <TT
CLASS="REPLACEABLE"
><I
>max-rows</I
></TT
>])</TT
></DT
><DD
><P
>       <TT
CLASS="LITERAL"
>spi_exec_query</TT
> executes an SQL command and
returns the entire row set as a reference to an array of hash
references.  <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>You should only use this command when you know
that the result set will be relatively small.</I
></SPAN
>  Here is an
example of a query (<TT
CLASS="COMMAND"
>SELECT</TT
> command) with the
optional maximum number of rows:

</P><PRE
CLASS="PROGRAMLISTING"
>$rv = spi_exec_query('SELECT * FROM my_table', 5);</PRE
><P>
        This returns up to 5 rows from the table
        <TT
CLASS="LITERAL"
>my_table</TT
>.  If <TT
CLASS="LITERAL"
>my_table</TT
>
        has a column <TT
CLASS="LITERAL"
>my_column</TT
>, you can get that
        value from row <TT
CLASS="LITERAL"
>$i</TT
> of the result like this:
</P><PRE
CLASS="PROGRAMLISTING"
>$foo = $rv-&gt;{rows}[$i]-&gt;{my_column};</PRE
><P>
       The total number of rows returned from a <TT
CLASS="COMMAND"
>SELECT</TT
>
       query can be accessed like this:
</P><PRE
CLASS="PROGRAMLISTING"
>$nrows = $rv-&gt;{processed}</PRE
><P>
      </P
><P
>       Here is an example using a different command type:
</P><PRE
CLASS="PROGRAMLISTING"
>$query = "INSERT INTO my_table VALUES (1, 'test')";
$rv = spi_exec_query($query);</PRE
><P>
       You can then access the command status (e.g.,
       <TT
CLASS="LITERAL"
>SPI_OK_INSERT</TT
>) like this:
</P><PRE
CLASS="PROGRAMLISTING"
>$res = $rv-&gt;{status};</PRE
><P>
       To get the number of rows affected, do:
</P><PRE
CLASS="PROGRAMLISTING"
>$nrows = $rv-&gt;{processed};</PRE
><P>
      </P
><P
>       Here is a complete example:
</P><PRE
CLASS="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 OR REPLACE FUNCTION test_munge() RETURNS SETOF test AS $$
    my $rv = spi_exec_query('select i, v from test;');
    my $status = $rv-&gt;{status};
    my $nrows = $rv-&gt;{processed};
    foreach my $rn (0 .. $nrows - 1) {
        my $row = $rv-&gt;{rows}[$rn];
        $row-&gt;{i} += 200 if defined($row-&gt;{i});
        $row-&gt;{v} =~ tr/A-Za-z/a-zA-Z/ if (defined($row-&gt;{v}));
        return_next($row);
    }
    return undef;
$$ LANGUAGE plperl;

SELECT * FROM test_munge();</PRE
><P>
    </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>spi_query(<TT
CLASS="REPLACEABLE"
><I
>command</I
></TT
>)</CODE
></TT
><BR><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>spi_fetchrow(<TT
CLASS="REPLACEABLE"
><I
>cursor</I
></TT
>)</CODE
></TT
><BR><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>spi_cursor_close(<TT
CLASS="REPLACEABLE"
><I
>cursor</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>    <TT
CLASS="LITERAL"
>spi_query</TT
> and <TT
CLASS="LITERAL"
>spi_fetchrow</TT
>
    work together as a pair for row sets which might be large, or for cases
    where you wish to return rows as they arrive.
    <TT
CLASS="LITERAL"
>spi_fetchrow</TT
> works <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>only</I
></SPAN
> with
    <TT
CLASS="LITERAL"
>spi_query</TT
>. The following example illustrates how
    you use them together:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TYPE foo_type AS (the_num INTEGER, the_text TEXT);

CREATE OR REPLACE FUNCTION lotsa_md5 (INTEGER) RETURNS SETOF foo_type AS $$
    use Digest::MD5 qw(md5_hex);
    my $file = '/usr/share/dict/words';
    my $t = localtime;
    elog(NOTICE, "opening file $file at $t" );
    open my $fh, '&lt;', $file # ooh, it's a file access!
        or elog(ERROR, "cannot open $file for reading: $!");
    my @words = &lt;$fh&gt;;
    close $fh;
    $t = localtime;
    elog(NOTICE, "closed file $file at $t");
    chomp(@words);
    my $row;
    my $sth = spi_query("SELECT * FROM generate_series(1,$_[0]) AS b(a)");
    while (defined ($row = spi_fetchrow($sth))) {
        return_next({
            the_num =&gt; $row-&gt;{a},
            the_text =&gt; md5_hex($words[rand @words])
        });
    }
    return;
$$ LANGUAGE plperlu;

SELECT * from lotsa_md5(500);</PRE
><P>
    </P
><P
>     Normally, <CODE
CLASS="FUNCTION"
>spi_fetchrow</CODE
> should be repeated until it
     returns <TT
CLASS="LITERAL"
>undef</TT
>, indicating that there are no more
     rows to read.  The cursor returned by <TT
CLASS="LITERAL"
>spi_query</TT
>
     is automatically freed when
     <CODE
CLASS="FUNCTION"
>spi_fetchrow</CODE
> returns <TT
CLASS="LITERAL"
>undef</TT
>.
     If you do not wish to read all the rows, instead call
     <CODE
CLASS="FUNCTION"
>spi_cursor_close</CODE
> to free the cursor.
     Failure to do so will result in memory leaks.
    </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>spi_prepare(<TT
CLASS="REPLACEABLE"
><I
>command</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>argument types</I
></TT
>)</CODE
></TT
><BR><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>spi_query_prepared(<TT
CLASS="REPLACEABLE"
><I
>plan</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>arguments</I
></TT
>)</CODE
></TT
><BR><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>spi_exec_prepared(<TT
CLASS="REPLACEABLE"
><I
>plan</I
></TT
> [, <TT
CLASS="REPLACEABLE"
><I
>attributes</I
></TT
>], <TT
CLASS="REPLACEABLE"
><I
>arguments</I
></TT
>)</CODE
></TT
><BR><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>spi_freeplan(<TT
CLASS="REPLACEABLE"
><I
>plan</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>    <TT
CLASS="LITERAL"
>spi_prepare</TT
>, <TT
CLASS="LITERAL"
>spi_query_prepared</TT
>, <TT
CLASS="LITERAL"
>spi_exec_prepared</TT
>,
    and <TT
CLASS="LITERAL"
>spi_freeplan</TT
> implement the same functionality but for prepared queries.
    <TT
CLASS="LITERAL"
>spi_prepare</TT
> accepts a query string with numbered argument placeholders ($1, $2, etc)
    and a string list of argument types:
</P><PRE
CLASS="PROGRAMLISTING"
>$plan = spi_prepare('SELECT * FROM test WHERE id &gt; $1 AND name = $2',
                                                     'INTEGER', 'TEXT');</PRE
><P>
    Once a query plan is prepared by a call to <TT
CLASS="LITERAL"
>spi_prepare</TT
>, the plan can be used instead
    of the string query, either in <TT
CLASS="LITERAL"
>spi_exec_prepared</TT
>, where the result is the same as returned
    by <TT
CLASS="LITERAL"
>spi_exec_query</TT
>, or in <TT
CLASS="LITERAL"
>spi_query_prepared</TT
> which returns a cursor
    exactly as <TT
CLASS="LITERAL"
>spi_query</TT
> does, which can be later passed to <TT
CLASS="LITERAL"
>spi_fetchrow</TT
>.
    The optional second parameter to <TT
CLASS="LITERAL"
>spi_exec_prepared</TT
> is a hash reference of attributes;
    the only attribute currently supported is <TT
CLASS="LITERAL"
>limit</TT
>, which sets the maximum number of rows returned by a query.
    </P
><P
>    The advantage of prepared queries is that is it possible to use one prepared plan for more
    than one query execution. After the plan is not needed anymore, it can be freed with
    <TT
CLASS="LITERAL"
>spi_freeplan</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE OR REPLACE FUNCTION init() RETURNS VOID AS $$
        $_SHARED{my_plan} = spi_prepare('SELECT (now() + $1)::date AS now',
                                        'INTERVAL');
$$ LANGUAGE plperl;

CREATE OR REPLACE FUNCTION add_time( INTERVAL ) RETURNS TEXT AS $$
        return spi_exec_prepared(
                $_SHARED{my_plan},
                $_[0]
        )-&#62;{rows}-&#62;[0]-&#62;{now};
$$ LANGUAGE plperl;

CREATE OR REPLACE FUNCTION done() RETURNS VOID AS $$
        spi_freeplan( $_SHARED{my_plan});
        undef $_SHARED{my_plan};
$$ LANGUAGE plperl;

SELECT init();
SELECT add_time('1 day'), add_time('2 days'), add_time('3 days');
SELECT done();

  add_time  |  add_time  |  add_time
------------+------------+------------
 2005-12-10 | 2005-12-11 | 2005-12-12</PRE
><P>
    Note that the parameter subscript in <TT
CLASS="LITERAL"
>spi_prepare</TT
> is defined via
    $1, $2, $3, etc, so avoid declaring query strings in double quotes that might easily
    lead to hard-to-catch bugs.
    </P
><P
>    Another example illustrates usage of an optional parameter in <TT
CLASS="LITERAL"
>spi_exec_prepared</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE hosts AS SELECT id, ('192.168.1.'||id)::inet AS address
                      FROM generate_series(1,3) AS id;

CREATE OR REPLACE FUNCTION init_hosts_query() RETURNS VOID AS $$
        $_SHARED{plan} = spi_prepare('SELECT * FROM hosts
                                      WHERE address &lt;&lt; $1', 'inet');
$$ LANGUAGE plperl;

CREATE OR REPLACE FUNCTION query_hosts(inet) RETURNS SETOF hosts AS $$
        return spi_exec_prepared(
                $_SHARED{plan},
                {limit =&gt; 2},
                $_[0]
        )-&#62;{rows};
$$ LANGUAGE plperl;

CREATE OR REPLACE FUNCTION release_hosts_query() RETURNS VOID AS $$
        spi_freeplan($_SHARED{plan});
        undef $_SHARED{plan};
$$ LANGUAGE plperl;

SELECT init_hosts_query();
SELECT query_hosts('192.168.1.0/30');
SELECT release_hosts_query();

    query_hosts    
-----------------
 (1,192.168.1.1)
 (2,192.168.1.2)
(2 rows)</PRE
><P>
    </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="SECT2"
><H2
CLASS="SECT2"
><A
NAME="PLPERL-UTILITY-FUNCTIONS"
>41.3.2. Utility Functions in PL/Perl</A
></H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>elog(<TT
CLASS="REPLACEABLE"
><I
>level</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>msg</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>       Emit a log or error message. Possible levels are
       <TT
CLASS="LITERAL"
>DEBUG</TT
>, <TT
CLASS="LITERAL"
>LOG</TT
>, <TT
CLASS="LITERAL"
>INFO</TT
>,
       <TT
CLASS="LITERAL"
>NOTICE</TT
>, <TT
CLASS="LITERAL"
>WARNING</TT
>, and <TT
CLASS="LITERAL"
>ERROR</TT
>.
       <TT
CLASS="LITERAL"
>ERROR</TT
>
        raises an error condition; if this is not trapped by the surrounding
        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 <TT
CLASS="LITERAL"
>die</TT
> command.
        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
        <A
HREF="runtime-config-logging.html#GUC-LOG-MIN-MESSAGES"
>log_min_messages</A
> and
        <A
HREF="runtime-config-logging.html#GUC-CLIENT-MIN-MESSAGES"
>client_min_messages</A
> configuration
        variables. See <A
HREF="runtime-config.html"
>Chapter 18</A
> for more
        information.
      </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>quote_literal(<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>        Return the given string suitably quoted to be used as a string literal in an SQL
        statement string. Embedded single-quotes and backslashes are properly doubled.
        Note that <CODE
CLASS="FUNCTION"
>quote_literal</CODE
> returns undef on undef input; if the argument
        might be undef, <CODE
CLASS="FUNCTION"
>quote_nullable</CODE
> is often more suitable.
      </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>quote_nullable(<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>        Return the given string suitably quoted to be used as a string literal in an SQL
        statement string; or, if the argument is undef, return the unquoted string "NULL".
        Embedded single-quotes and backslashes are properly doubled.
      </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>quote_ident(<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>        Return the given string suitably quoted to be used as an identifier in
        an SQL statement string. Quotes are added only if necessary (i.e., if
        the string contains non-identifier characters or would be case-folded).
        Embedded quotes are properly doubled.
      </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>decode_bytea(<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>        Return the unescaped binary data represented by the contents of the given string,
        which should be <TT
CLASS="TYPE"
>bytea</TT
> encoded.
        </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>encode_bytea(<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>        Return the <TT
CLASS="TYPE"
>bytea</TT
> encoded form of the binary data contents of the given string.
        </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>encode_array_literal(<TT
CLASS="REPLACEABLE"
><I
>array</I
></TT
>)</CODE
></TT
><BR><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>encode_array_literal(<TT
CLASS="REPLACEABLE"
><I
>array</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>delimiter</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>        Returns the contents of the referenced array as a string in array literal format
        (see <A
HREF="arrays.html#ARRAYS-INPUT"
>Section 8.15.2</A
>).
        Returns the argument value unaltered if it's not a reference to an array.
        The delimiter used between elements of the array literal defaults to "<TT
CLASS="LITERAL"
>, </TT
>"
        if a delimiter is not specified or is undef.
        </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>encode_typed_literal(<TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>, <TT
CLASS="REPLACEABLE"
><I
>typename</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>         Converts a Perl variable to the value of the data type passed as a
         second argument and returns a string representation of this value.
         Correctly handles nested arrays and values of composite types.
       </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>encode_array_constructor(<TT
CLASS="REPLACEABLE"
><I
>array</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>        Returns the contents of the referenced array as a string in array constructor format
        (see <A
HREF="sql-expressions.html#SQL-SYNTAX-ARRAY-CONSTRUCTORS"
>Section 4.2.12</A
>).
        Individual values are quoted using <CODE
CLASS="FUNCTION"
>quote_nullable</CODE
>.
        Returns the argument value, quoted using <CODE
CLASS="FUNCTION"
>quote_nullable</CODE
>,
        if it's not a reference to an array.
        </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>looks_like_number(<TT
CLASS="REPLACEABLE"
><I
>string</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>        Returns a true value if the content of the given string looks like a
        number, according to Perl, returns false otherwise.
        Returns undef if the argument is undef.  Leading and trailing space is
        ignored. <TT
CLASS="LITERAL"
>Inf</TT
> and <TT
CLASS="LITERAL"
>Infinity</TT
> are regarded as numbers.
        </P
></DD
><DT
><TT
CLASS="LITERAL"
><CODE
CLASS="FUNCTION"
>is_array_ref(<TT
CLASS="REPLACEABLE"
><I
>argument</I
></TT
>)</CODE
></TT
></DT
><DD
><P
>        Returns a true value if the given argument may be treated as an
        array reference, that is, if ref of the argument is <TT
CLASS="LITERAL"
>ARRAY</TT
> or
        <TT
CLASS="LITERAL"
>PostgreSQL::InServer::ARRAY</TT
>.  Returns false otherwise.
      </P
></DD
></DL
></DIV
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