Welcome to Perl. May you find the enjoyment I have in working with it.

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If I am reading your question correctly, you want to execute two SQL statements that exist as string constants in your code. Your issue is that your second assignment to the variable $sql overwrites the first assignment. There are a number of ways to address this, but I think the most logical would be assigning to an array rather than a scalar and then looping over those values. Something like:

use strict;
use warnings;

sub create_temp_tables($$) {
    # Create copies of sp047 and sp057 for updating
    my ($dbh, $dbms) = (@_);
    my @sqls;
    if ($dbms eq 'ORACLE') {
        push @sqls, q{create table sp047_postcodes_temp as select * fr
+om sp047_postcodes};
        push @sqls, q{create table sp057_regions_temp as select * from
+ sp057_regions};
    } else # SQLServer
    {
        push @sqls, q{select * into sp047_postcodes_temp from sp047_po
+stcodes};
        push @sqls, q{select * into sp057_regions_temp from sp057_regi
+ons};
    }
    foreach my $sql (@sqls) {
        my $sth = $dbh->prepare($sql);
        if ($sth) {
            my $rc = $sth->execute();
            if ($sth->err) {
                myexit($sth->errstr, $dbh);
            } else { # Need to commit to release locks in SQL Server -
+ we have done nothing else at this stage,
                # so no problem with this.
                $dbh->commit;
            }
            $sth->finish;
        } else {
            myexit("Unable to prepare SQL : " . $sql . "\n", $dbh);
        }
    }
}
[download]

You can learn more about the data types in Perl from perldata and basic Perl control structures from perlsyn. There are a number of elements of your code that don't generally follow "best practice", like your prototyping (subroutine prototype in Perl), so you might take a few minutes to peruse the archives here to learn a bit about normal structures. Hope this helps, and please ask follow-up questions if this is unclear.