Is it possible to have a DISTICT statement only on one varible? - php

Question

I only want the SELECT DISTINCT statement on 'yearLevel' (as I don't want any duplicates only on yearLevel)
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For example I only want one 'yearLevel' 12 record in the table, and for that to be the one with the lowest 'totalSeconds'
code
$sql = "SELECT firstName, lastName, yearLevel, totalSeconds
FROM studentInformation
JOIN record
ON studentInformation.studentId = record.student_Id
ORDER BY totalSeconds ASC
LIMIT 1 ";
Is it possible to do this -
$sql = "SELECT firstName, lastName, DISTINCT yearLevel, totalSeconds
FROM studentInformation
JOIN record
ON studentInformation.studentId = record.student_Id
ORDER BY totalSeconds ASC
LIMIT 1 ";

Answer 1

Provided that "firstName" and "lastName" are in table "studentInformation", and "yearLevel" as well as "totalSeconds" are in table "record" this query should be working. It uses a correlated subquery. I did not test this; if it doesn't work please let me know.
SELECT a.firstName, a.lastName, b.yearLevel, b.totalSeconds
FROM studentInformation a
INNER JOIN record b ON a.studentId = b.studentId
WHERE b.totalSeconds = ( SELECT min(totalSeconds)
FROM record
WHERE yearLevel = b.yearLevel )
ORDER BY b.totalSeconds ASC
Assuming that only "totalSeconds" is in table "record" this could work, too.
SELECT a.firstName, a.lastName, a.yearLevel, b.totalSeconds
FROM studentInformation a
INNER JOIN record b ON a.studentId = b.studentId
WHERE b.totalSeconds = ( SELECT MIN(d.totalSeconds)
FROM studentInformation c
INNER JOIN record d ON c.studentId = d.studentId
WHERE c.yearLevel = a.yearLevel )
ORDER BY b.totalSeconds ASC