MySQL query seems to give different results when wrapped in perl DBI - mysql

Question

The query below works fine in when I try it in the console.
mysql> SELECT COUNT(l.ID), a.MAX_PER_PRD, a.PLURAL, d.TIME_DENOM FROM logro l, challenge c, lib_accomp_type a, lib_deporte d WHERE l.PERIOD=3 AND l.GAME_ID=2 AND l.PLR_ID=3 AND l.ACC_TYPE_ID=11 AND a.sport=d.ID AND c.ACC_TYPE_ID=a.ID AND l.ACC_TYPE_ID=c.ACC_TYPE_ID;
+-------------+-------------+--------------------+------------+
| COUNT(l.ID) | MAX_PER_PRD | PLURAL | TIME_DENOM |
+-------------+-------------+--------------------+------------+
| 0 | 3 | general commodities| quarter |
+-------------+-------------+--------------------+------------+
1 row in set (0.01 sec)
However, when I wrap it in a perl->DBI statement handle and fetch it with $sth->fetchrow_array the second value is undefined.
my $q = "SELECT COUNT(l.ID), a.MAX_PER_PRD, a.PLURAL, d.TIME_DENOM
FROM logro l, challenge c, lib_accomp_type a, lib_deporte d
WHERE l.PERIOD=?
AND l.GAME_ID=?
AND l.PLR_ID=?
AND l.ACC_TYPE_ID=?
AND a.sport=d.ID
AND c.ACC_TYPE_ID=a.ID
AND l.ACC_TYPE_ID=c.ACC_TYPE_ID";
my $sth = $dbh->prepare($q);
$sth->execute(3, 2, 3, 11);
my ($CNT, $MAX, $ANAMEP, $TD) = $sth->fetchrow_array;
print "COUNT: ", $CNT;
print "MAX: ", $MAX;
$ perl test_sql2.pl
Use of uninitialized value $MAX in print at test_sql2.pl line 29.
COUNT: 0MAX:
Any idea as to what I could be doing wrong?

Answer 1

Depending on your mysql client/library version, mysql handles this situation differently.
For mysql <= 5.6, see Group By Handling
For mysql = 5.7, see Group By Handling
You query has a count of 0, yet there are values returned for the other columns. That doesn't seem to make any sense. It seems that running through perl is actually doing the logical thing and mysql is just populating the MAX_PER_PRD, PLURAL, TIME_DENOM columns with arbitrary values.
The main issue here, is that you referencing non-aggregated columns without them being part of a group by clause.
Perhaps if you include a sample data set, it could help us get to the result your are looking for.