Question

From the SQL::Statement::Functions documentation:

Creating User-Defined Functions
…
More complex functions can make use of a number of arguments always passed to functions automatically. Functions always receive these values in @_:
sub FOO { my( $self, $sth, $rowhash, @params ); }

#!/usr/bin/env perl
use 5.012;
use warnings; use strict;
use DBI;

my $dbh = DBI->connect( "DBI:CSV:", undef, undef, { RaiseError => 1, } );
my $table = 'wages';
my $array_ref = [   [ 'id', 'number' ],  
            [ 0, 6900 ], 
            [ 1, 3200 ], 
            [ 2, 1800 ],    ];

$dbh->do( "CREATE TEMP TABLE $table AS import( ? )", {}, $array_ref );

sub routine {
    my $self = shift;
    my $sth = shift;
    my $rowhash = shift; #
    return $_[0] / 30; 
};

$dbh->do( "CREATE FUNCTION routine" );
my $sth = $dbh->prepare( "SELECT id, routine( number ) AS result FROM  $table" );
$sth->execute();
$sth->dump_results();

When I try this I get an error-message:

DBD::CSV::st execute failed: Use of uninitialized value $_[0] in division (/) at ./so.pl line 27.
[for Statement “SELECT id, routine( number ) AS result FROM “wages””] at ./so.pl line 34.

When I comment out the third argument I works as expected ( because it looks as if the third argument is missing ):

#!/usr/bin/env perl
...  
sub routine {
    my $self = shift;
    my $sth = shift;
    #my $rowhash = shift;
    return $_[0] / 30; 
};
...

0, 230
1, 106.667
2, 60
3 rows

Is this a bug?

Answer 1

Also from the SQL::Statement::Functions documentation:

When using
SQL::Statement/SQL::Parser directly to
parse SQL, functions (either
built-in or user-defined) may occur
anywhere in a SQL statement that
values, column names, table names, or
predicates may occur. When using
the modules through a DBD or in any
other context in which the SQL is
both parsed and executed, functions
can occur in the same places except
that they can not occur in the column
selection clause of a SELECT
statement that contains a FROM clause.

i.e.

SELECT id, routine( number ) AS result FROM  wages

will not work.

Rewrite your function to return a table, something like this:

sub routine {
    my($self,$sth,$rowhash,@params) = @_;
    return [ [qw(id result)],
             map { [ $_->[0], $_->[1] / 30 ] } @$array_ref ];
};

$dbh->do( "CREATE FUNCTION routine" );
my $sth = $dbh->prepare( "SELECT * FROM routine()" );
$sth->execute();
$sth->dump_results();

With the expected results:

$ perl dl.pl 
0, 230
1, 106.667
2, 60
3 rows