MySQL显示分组结果

Question

I have the following snippet of a table:

stamp   | group  | value
 123     | 1      | 4
 124     | 2      | 5
 124     | 2      | 6
 125     | 4      | 7
 125     | 4      | 8
 125     | 5      | 9

I can't seem to find a query that gives me this result:

stamp   | value1  | value2
 124     | 5       | 6
 125     | 7       | 8
 125     | 9       | null

So basically, all results with the same stamp are shown, grouped by 'group'. Is this possible ? I've tried to accomplish this with subqueries, 'group by' and 'having' statements, but I can't seem to find the right query..

Thnx in advance !

Answer 1

I think you need something like this, more or less:

SELECT stamp, `group`, GROUP_CONCAT(`value`) AS `values`
FROM stamps
GROUP BY stamp, `group`

The key is GROUP_CONCAT .

Based on your data the output will be

+-------+-------+--------+
| stamp | group | values |
+-------+-------+--------+
|   123 |     1 | 4      |
|   124 |     2 | 5,6    |
|   125 |     4 | 7,8    |
|   125 |     5 | 9      |
+-------+-------+--------+

Answer 2

select stamp, 
       SUBSTR(`values`,1,INSTR(`values`,',')-1) as value1,
       NULLIF(TRIM(',' FROM SUBSTR(`values`,INSTR(`values`,',')+1)),'') as value2,
       `values`
FROM
(
SELECT stamp, `group`,CONCAT( GROUP_CONCAT(`value`) ,',') AS `values`
FROM stamps
GROUP BY stamp, `group`
) aggr

Fiddle Demo

This works only when every group has <=2 rows only.