MySQL INNER JOIN with SubQuery (well detailed) - mysql

Question

I'm trying to add a third INNER JOIN to a SELECT Query, where this third INNER JOIN needs to look for a value in that third Table, which value needs to be coupled with the outcome of a MAX + GROUP BY construct in the main SELECT Query. This may not be possible, I don’t know. I can't get it to work :-)
Example
TableA
User - Score
userA - 10
userB - 42
userC - 32
userB - 42
userB - 18
userD - 12
userB - 65
.
Table B
User - Color
userA - Green
userB - Yellow
userC - Blue
On these two tables I use a
SELECT
MAX(TableA.Score) AS MaxScore,
TableB.Color
FROM TableA
INNER JOIN TableB
ON TableA.User = TableB.User
GROUP BY TableA.User
The output here works nicely and is
User - MaxScore - Color
UserA - 10 - Green
UserB - 65 - Yellow
UserC - 32 - Blue
Now, I have a separate table where all the Scores get names.
TableC
Score - Name
5 - Quite Low
10 - OK
25 - Not bad
32 - Fairly good
50 - Well done
65 - Excellent
What I try to do is get a QUERY result which reads…
User - MaxScore - Name - Color
UserA - 10 - OK - Green
UserB - 65 - Excellent - Yellow
UserC - 32 - Fairly Good - Blue
My QUERY would look something like this…
SELECT
TableA.User
MAX(TableA.Score) AS MaxScore,
TableC.Name,
TableB.Color
FROM TableA
INNER JOIN TableB
ON TableA.User = TableB.User
INNER JOIN TableC
ON TableC.Score = (SELECT MAX(TableA.Score) AS MaxScore FROM Table A GROUP BY TableA.User) ThisSubQueryName
GROUP BY TableA.User
My problem is clearly with the syntax of the INNER JOIN of Table C, which INNER JOIN carries that subquery. I have no idea how to do this, or if it is even possible.
Looking forward to your wisdom.
Thanks :-)
Dutch

Answer 1

Try this instead:
SELECT mainQ.*, c.Name
FROM (
SELECT a.`User`, MAX(a.Score) AS MaxScore, b.Color
FROM TableA AS a
INNER JOIN TableB AS b ON a.`User` = b.`User`
GROUP BY a.`User`
) AS mainQ
INNER JOIN TableC AS c
ON mainQ.MaxScore = c.Score
Though your subquery could've worked with some modifications (involving table aliases and replacing it's GROUP BY with a WHERE), correlated subqueries are relatively expensive and often unnecessary.
Edit: Wow, after all that, I just realized I basically duplicated scaisEdge's answer's query; amazing how much a couple newlines can throw off your skimming ability.

Answer 2

You should use a dinamic table(t) and then the inner join on TableC
select t.User, t.MaxScore, c.Name, t.Color from (
SELECT
TableA.User as User
MAX(TableA.Score) AS MaxScore,
TableB.Color as Color
FROM TableA
INNER JOIN TableB
ON TableA.User = TableB.User
GROUP BY TableA.User
) t
INNER JOIN TableC on t.MaxScore = TableC.Score