How to group by a column with forloop and union all - php

Question

Hi this is my query from this query i am getting 3 records i want only one record and i am trying to group by studentid
foreach ($gdFinaldata['gdskill'] as $skillId => $skillScore){
$filterQuery .= $union_all. "SELECT stu.student_pid
FROM tbl_students stu LEFT JOIN r_job_invitations jbi ON stu.student_email = jbi.email
LEFT JOIN r_job_scores jsc ON jsc.student_id = stu.student_pid
WHERE job_id = ".$jobID." AND skill_id = ".$skillId." AND gd_score >= ".$skillScore." ";
$union_all=" UNION ALL ";
} //for ends here
the recodrs will come like this:
SELECT stu.student_pid FROM tbl_students stu LEFT JOIN r_job_invitations jbi ON stu.student_email = jbi.email LEFT JOIN r_job_scores jsc ON jsc.student_id = stu.student_pid WHERE job_id = 88 AND skill_id = 3 AND gd_score >= 1
UNION ALL
SELECT stu.student_pid FROM tbl_students stu LEFT JOIN r_job_invitations jbi ON stu.student_email = jbi.email LEFT JOIN r_job_scores jsc ON jsc.student_id = stu.student_pid WHERE job_id = 88 AND skill_id = 63 AND gd_score >= 2
UNION ALL
SELECT stu.student_pid FROM tbl_students stu LEFT JOIN r_job_invitations jbi ON stu.student_email = jbi.email LEFT JOIN r_job_scores jsc ON jsc.student_id = stu.student_pid WHERE job_id = 88 AND skill_id = 128 AND gd_score >= 3
After this i want to add group by how can i do that i tried like this:
$groupby = "GROUP BY student_id";
$filterStudents = $conn->query($filterQuery.$groupby);
My issue is still returning 3 records i want to group by student
For Reference:

Answer 1

There are several ways to do this.
Use union instead of union all, this will retain only unique entries
select ...
union
select ...
union
select ...
If you want to keep union all (why do you?), use parenthesis around your selects and append group by after it
select student_pid
( select student_pid, student_id from ...
union all
select student_pid, student_id from ...
union all
select student_pid, student_id from ... ) as t
group by student_id
Your PHP would then look like
foreach (...) {
$filterQuery .= $union_all. "SELECT stu.student_pid, jsc.student_id ..."
// ...
}
$outerQuery = "select student_pid ("
$groupby = ") as t GROUP BY student_id";
$filterStudents = $conn->query($outerQuery . $filterQuery . $groupby);
Instead of group by, you can also use distinct, e.g.
select distinct student_pid
( select student_pid from ...
union all
select student_pid from ...
union all
select student_pid from ... ) as t
Collect the result in an array and then use array_unique
Although this is the least efficient, since it fetches all entries instead of the relevant parts.