SQL concat IDs of rows after group by

Question

I'm trying to output a query that has a count of a group by but also, specifies the list of IDs in that row.

This is what I have so far:

SELECT
    title,
    period,
    COUNT(*)
FROM
    table
GROUP BY
    title, period

Example database

Title	Period	ID
Title2	MONTH	321
Title1	DAY	789
Title1	DAY	123
Title1	MONTH	123

Output

Title	Period	COUNT(*)
Title2	MONTH	1
Title1	DAY	2
Title1	MONTH	1

But I would like the output to be something like:

Title	Period	COUNT(*)	Who?
Title2	MONTH	1	321
Title1	DAY	2	123, 789
Title1	MONTH	1	123

What do I need to add to my query to get this output? I've tried to use an SELF JOIN and a SELECT JOIN, but I cannot quite get the syntax right.

Answer 1

We can use GROUP_CONCAT:

SELECT
    title,
    period,
    COUNT(*),
    GROUP_CONCAT(id ORDER BY id separator ', ') AS Who
FROM
    yourtable
GROUP BY
    title, period
ORDER BY title DESC;

Note: I don't know if the two ORDER BY clauses are necessary for you. I just added them to produce exactly your outcome. Remove them if not needed.

You can also remove the "separator ', ') part if you don't require spaces after the comma.

Try out: db<>fiddle

Here the documentation: documentation