Question

I have two queries I want to combine into a single output, I can’t use a UNIOn because they have different numbers of columns.

The table is ref with fields id refid cellid cat all of which contain whole numbers

Query 1: Finds the total number of rows for each unique cellid

SELECT cellid, COUNT(*) totalcount, cat FROM rel GROUP BY cellid

Query 2: Finds the Mode (most common value) of cat for each unique cellid

SELECT cellid, cat
FROM rel t
GROUP BY cellid, cat
HAVING cat = (
SELECT cat
FROM rel
WHERE cellid = t.cellid
GROUP BY cat
ORDER BY COUNT(*) DESC, cat
LIMIT 1
)

To give an example of what I’m trying to do I want to query my table

id | refid | cellid | cat
1  | 1     |  1     | 1
2  | 2     |  2     | 2
3  | 3     |  3     | 4
4  | 1     |  1     | 2
5  | 2     |  1     | 2
6  | 3     |  1     | 3
7  | 1     |  2     | 2
8  | 1     |  1     | 2

and return

cellid | no_of_rows | Mode_of_cat
 1     |  5         |  2
 2     |  2         |  2
 3     |  1         |  4

Answer 1

The easiest solution here is just to write a query to join the two result sets you already have. You can store the result of your queries in tmp tables and join the temp tables like so:

SELECT tmp1.cellid, tmp1.rows, tmp2.mode_cat FROM
(
    SELECT cellid, COUNT(*) AS rows
    FROM rel
    GROUP BY cellid
)tmp1
LEFT JOIN
(
    SELECT cellid, cat AS mode_cat
    FROM rel t
    GROUP BY cellid, cat
    HAVING cat = (
        SELECT cat
        FROM rel
        WHERE cellid = t.cellid
        GROUP BY cat
        ORDER BY COUNT(*) DESC, cat
        LIMIT 1
    )
)tmp2
ON tmp1.cellid = tmp2.cellid;