You're performing the query and the fetch in a single step. Every time the loop executes you repeat the query and the fetch starts back at the beginning.

You have to execute the query outside the loop, then execute the FetchRow within the loop

my $q = $dbh->Query("select s.sect, s.test, t.name, t.res_tbl t.f_num 
+fro
+m s_lab_recs s, tests t where s.s_lab_id=$id and s.sect=t.sect_id");

while(my @row = $q->FetchRow) {
    push @sect, $row[0];
    push @test, $row[1];
}
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