(I'm assuming that the two databases aren't linked, i.e. you can't join their tables. I'm also assuming that you're using DBI despite the mention of a fetchrow function. (DBI has fetchrow_arrayref, fetchrow_array, and fetchrow_hashref, but no just plain fetchrow.))

If you don't need the even ids from studentTable why not add a where clause to return only the odds?

If all you're doing with the studentTable in the 1st DB is loading an array why not use fetchall_arrayref?

my $studentInfo = $sth_queryID->fetchall_arrayref;
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If you do need the even ids elsewhere you can easily skip them when querying the grades in the 2nd DB like this:

for my $studentInfo_row (@{$studentInfo}) {
  next unless $studentInfo_row->[0] % 2;
  ...
}
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You could also use a grep:

foreach my $studentInfo_row ( grep { $_->[0] % 2 } @{$studentInfo}) {
  ...
}
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update: fixed arrayref typos