The steps in using a statement hanlde are prepare, exectue, and fetch, not do and fetch:

my $sth = $dbh->prepare( $sql );
$sth->execute;
my @array = $sth->fetchrow_array;
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Note also that fetchrow_array returns, as it says, an array so the return should be assigned to an array, not a scalar. Also note that this will only fetch one row. If you want more rows you need to do the fetchrow_array() inside a loop.