What do you see when you stare & compare?
SELECT
LKC.combo, lockCombo1
FROM [Inputtb] A
JOIN test.dbo.School SCH
ON A.schoolnumber = SCH.type
and A.schoolnumber = @SchoolNumber
JOIN test.dbo.Locker LKR
ON SCH.schoolID = LKR.schoolID
AND A.lockerNumber = LKR.number
and LKR.schoolID = @SchoolID
JOIN test.dbo.Lock LK
ON LKR.lockID = LK.lockID
JOIN test.dbo.LockCombination LKC
ON LK.lockID = LKC.lockID
WHERE LKC.seq = 1
--AND LKC.combo <> lockCombo1
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden