Question

How do I get all the values in a group by statement?

mysql>select * from mytable;
+------+--------+--------+
| name | amount | status |
+------+--------+--------+
| abc  |     12 | A      | 
| abc  |     55 | A      | 
| xyz  |     12 | B      | 
| xyz  |     12 | C      | 
+------+--------+--------+
4 rows in set (0.00 sec)

mysql>select name, count(*) from mytable where status = 'A' group by name;
+------+----------+
| name | count(*) |
+------+----------+
| abc  |        2 | 
+------+----------+
1 row in set (0.01 sec)

Expected result:

+------+----------+
| name | count(*) |
+------+----------+
| abc  |        2 | 
| xyz  |        0 | 
+------+----------+

Answer 1

There’s a funny trick you can use where COUNT(column) counts the number of non-null values; you also use a self-join (when doing this):

SELECT a.name, COUNT(b.name)
  FROM mytable AS a LEFT OUTER JOIN mytable AS b
    ON a.name = b.name AND b.status = 'A'
 GROUP BY a.name;

This would work in all versions of SQL; not all variants will allow you to sum on a Boolean expression, which is undoubtedly faster and more direct when supported.

Another way to write it is:

SELECT a.name, COUNT(b.name)
  FROM mytable AS a LEFT OUTER JOIN
       (SELECT name FROM mytable WHERE status = 'A') AS b
    ON a.name = b.name
 GROUP BY a.name;