If you go the manual method, you can use something like this:

my $ingres_dbh  = DBI->connect( @ingres_connection_args );
my $mysql_dbh   = DBI->connect( @mysql_connection_args  );
my @sql = (
    { select => 'SELECT f1,f2,f3 FROM master_table_1'
    , insert => 'INSERT INTO back_table_2(f1,f2,f3) VALUES(?,?,?)'
    }
    ,
    { select => 'SELECT abc1,abc2,abc3 FROM master_table_2'
    , insert => 'INSERT INTO back_table_2(abc1,abc2,abc3) VALUES(?,?,?
+)'
    }
);
for( 0..1 ){
    my $select = $ingres_dbh->prepare( $sql[$_]->{select} );
    my $insert = $mysql_dbh->prepare(  $sql[$_]->{insert} );,
    while(my $row = $select->fetch){
        $insert->execute(@$row);
    }
}
[download]

If you're doing a one-time transfer between two databases, it sounds to me like Perl might not be a great choice. What I would do is find out how to use the bulk loading facility in whatever your target database is. Then write a query to extract the data from the first database and save it to a file in the correct format for the second databases' bulk load program. Actually, for this purpose Perl might be a good choice. If you are writing a text file, a module like Text::Template or Text::CSV depending on how fancy it is.

If you do decide to go the straight Perl way, you should at a minimum use pleaceholders for the insertion step. Something like

my $sth_insert = $dbh2->prepare("insert into back_table_2 (abc1,abc2,a
+bc3)                  
                                   VALUES (?, ?, ?) ");
while ($row = $sth->fetchrow_arrayref) {
    $sth_insert->execute(@$row);
}
[download]

/J