MySQL Operand should contain 1 column - how to overcome - mysql

Question

I have the following MySQL code:
SELECT company, ((AVG (q1) + AVG(q2) + AVG(q3) ) / 3) AS High,
(SELECT company, ((AVG (q1) + AVG(q2) + AVG(q3) ) / 3)
FROM tresults_new GROUP BY company ASC LIMIT 1) AS Low
FROM tresults_new GROUP BY company DESC LIMIT 1
Now I understand why this brings back the error in the title, as I am bringing back both company and Low in the subquery.
What I am struggling with is how to return both the High and Low (or if you prefer Max and Min) in a single query and I cannot fathom if it is possible and how I would go about it.
Any and all suggestions and feedback welcomed.
For reference, table structure:
company q1 q2 q3
abc 5 6 2
abc 9 5 8
xyz 3 4 6
xyz 3 2 1
zyx 7 9 10

Answer 1

Using the max and min functions should help. I tend to work in SQL Server but this should be true for MySQL as well.
UPDATED AFTER FURTHER CLARIFICATION
So after all the comments on both my response. OPs post and another response. I fiddled around a bit and this should actually get you what you want. It's possibly overblown if you are only doing this once but if your data set grows large this should accomplish what you need and still give you the max and min values that you desire so you know your highest and lowest performing companies. I also did a SQLFiddle if you want to play with it yourself - to be clear I used SQL Server because I'm more familiar in the fiddle example but any changes to MySQL should be relatively trivial.
SELECT vals.company, vals.myval
FROM
(SELECT company, ((AVG (q1) + AVG(q2) + AVG(q3) ) / 3) as myval
FROM tresults_new GROUP BY company
) vals
INNER JOIN
(
SELECT max(myval) val
FROM
(SELECT company, ((AVG (q1) + AVG(q2) + AVG(q3) ) / 3) as myval
FROM tresults_new GROUP BY company
) s
UNION
SELECT min(myval) val
FROM
(SELECT company, ((AVG (q1) + AVG(q2) + AVG(q3) ) / 3) as myval
FROM tresults_new GROUP BY company
) s
) maxmin on maxmin.val = vals.myval

Answer 2

I don't think that you can reasonably avoid two queries or it would be a subquery which leaves you no better off. From your comment and your sample query, I understand that you're just interested in which company has the highest value of AVG(q1)+AVG(q2)+AVG(q3) and which other has the lowest value thereof. In this case I'd just rely on a single query ordered by this value. The first and last rows will be your answer.
SELECT company, val FROM
(SELECT company, AVG(q1) + AVG(q2) + AVG(q3) AS val
FROM tresults_new
GROUP BY company
ORDER BY val DESC LIMIT 1)
AS VAL_MAX
UNION
SELECT company, val FROM
(SELECT company, AVG(q1) + AVG(q2) + AVG(q3) AS val
FROM tresults_new
GROUP BY company
ORDER BY val ASC LIMIT 1)
AS VAL_MIN
or just one query without LIMIT clause and get the first and last rows.
Warning: Of course, it would be tempting to write something like:
SELECT company, MIN(val), MAX(val) FROM
(SELECT company, AVG(q1) + AVG(q2) + AVG(q3) AS val
FROM tresults_new
GROUP BY company)
AS values [GROUP BY company]
without the last GROUP BY company, you'll get the min the max but not the company (this query would be accepted by MySQL but rejected by a number of other RDBMS because you need explicit grouping).
So add the GROUP BY and you'll just get the same values for both min and max which leaves you no better off than your inner query.