SQL OR clause priority - mysql

Question

I have a table with user awards, which can be of various different types.
For example, here are the records for the qualification ID 94:
So as you can see, there are 2 users, one has records for the award type of "average", "min", "max" and "final", the other has the same but no "final" award.
What I want is to get only 1 row per user. If they have an award of type "final" I want that, otherwise I want the "average" one, I don't want "min" or "max" at all.
So as an example, here is the query with just a simple IN clause:
So based on that, what I want the result to be is for the user 34562 I want the row with the "final" award, and for the user 6256 i want the row with their "average" award, since they don't have a "final" record.
I'm sure this should be fairly simple, but i'm failing miserably this morning.
I think I should be able to select the final record, then do a UNION ALL, but I can't seem to work it out in my head. Can anyone point me in the right direction?
I should point out that whilst this is MySQL for me, it needs to be compatible with other database platforms.
Thanks.

Answer 1

An easy way would be to check if an average entry exists in the where clause:
SELECT * FROM Table t
WHERE qualid = 94
and (type = 'average' AND
not exists(SELECT * FROM Table t2
WHERE t.qualid=t2.qualid AND t.userid=t2.userid AND type = 'final')
OR type = 'final')

Answer 2

You can accomplish this using MySQL user defined variables which will be more scalable.
SELECT
t.*
FROM
(
SELECT
*,
IF(#sameUser = userid, #rn := #rn + 1,
IF(#sameUser := userid, #rn := 1,#rn := 1)
) AS row_number
FROM moodle.mdl_bcgt_user_qual_awards
CROSS JOIN (SELECT #sameUser := -1, #rn := 1) AS var
WHERE qualid = 94
AND type IN ('final','average')
ORDER BY userid,
CASE WHEN type = 'final' THEN 0 ELSE 1 END
) AS t
WHERE t.row_number <= 1
ORDER BY t.userid
EDIT:
using NOT EXISTS & UNION ALL
SELECT
*
FROM your_table
WHERE qualid = 94
AND type = 'final'
UNION ALL
SELECT
*
FROM your_table A
WHERE qualid = 94
AND type = 'average'
AND NOT EXISTS (
SELECT 1 FROM your_table B WHERE A.qualid = B.qualid AND B.userid = A.userid AND B.type = 'final'
)

Answer 3

You can try this for sql Server
Select * from (
SELECT *,ROW_NUMBER() over(PARTITION BY type ORDER BY type) rowNo
FROM mdl_bcgt_user_qual_awards
WHERE qualid = 94
AND type in ('final','average')
Order By type
) as t
Where rowNo=1
Hear we have done Order by on type as character meet our requirement if any other text then just add case and sort on the basis of that field.

Answer 4

Here is a pure MySQL solution, which should also be generally ANSI compliant across most RDBMS:
SELECT t1.*
FROM yourTable t1
INNER JOIN
(
SELECT qualid,
CASE WHEN MAX(CASE WHEN type = 'final' THEN 100
WHEN type = 'average' THEN 10
ELSE 1
END) = 100 THEN 'final'
WHEN MAX(CASE WHEN type = 'final' THEN 100
WHEN type = 'average' THEN 10
ELSE 1
END) = 10 THEN 'average'
ELSE NULL
END AS type
FROM yourTable
GROUP BY qualid
) t2
ON t1.qualid = t2.qualid AND
t1.type = t2.type
This query employs a trick, which is to aggregate a sum for each qualid group based on whether final, average, or neither be present. I assign a value of 100 for final, 10 for average, and 1 for neither. This allows us to assign a type to each group.