Question

I have two tables:

Table alpha:

ID | Name
---------
1  | A
2  | B
3  | C

Table beta:

ID | state
----------
1  | 1
1  | 2
1  | 2
2  | 1

I would like to get a result like the following:

ID | Count(state=1) | Count (state=2)
-------------------------------------
1  | 1              | 2
2  | 1              | 0
3  | 0              | 0

How do I do this with SQL?
I can get the table without the result of ID 3, but that is not what I want.

Thanks in advance!

Answer 1

SELECT a.ID,
       SUM(CASE WHEN b.state = 1 THEN 1 ELSE 0 END) AS State1Count,
       SUM(CASE WHEN b.state = 2 THEN 1 ELSE 0 END) AS State2Count
    FROM alpha a
        LEFT JOIN beta b
            ON a.ID = b.ID
    GROUP BY a.ID