Question

Given a table of exam results, where 1 == PASS and 0 == FAIL

ID    Name    Test   Result
--------------------
1     John    MATH   1
2     John    ENGL   1
3     Mary    MATH   1
4     Mary    PSYC   0

EDIT: assume that the name is unique.

I need to get all records for people who

1) passed all tests
2) failed at least one test

So, the 1st query should return John and all his records, and the 2nd query should return Mary and all her records (including the ones with PASS).

I’m trying to do a LEFT OUTER JOIN with itself and compare counts, but don’t seem to get a working query.

SELECT * FROM Results R1
LEFT OUTER JOIN Results R2 on R1.ID=R2.ID and R2.Result=1
WHERE ??? count of rows from R1 is compared to count of non-null rows from R2

Answer 1

This is a “poster-child” exercise for the EXISTS clause:

At leasr one failed result:

select * from Results r
where exists (select * from Results rr where rr.Name=r.Name AND Result=0)

All passed:

select * from Results r
where not exists (select * from Results rr where rr.Name=r.Name AND Result=0)

See how these queries work on your data set at sqlfiddle.com.