Question

我有一个像这样的MySQL：

+----+----------+---------+---------------------+
| id | event    | seconds | date                |
+----+----------+---------+---------------------+
|  5 | open     |      0  | 2014-10-20 16:00:00 |
|  5 | assign   |      5  | 2014-10-20 16:00:05 |
|  5 | complete |     10  | 2014-10-20 16:00:15 |
|  5 | close    |     22  | 2014-10-20 16:00:37 |
|  6 | open     |      0  | 2014-10-20 17:00:00 |
|  6 | assign   |      7  | 2014-10-20 17:00:07 |
+----+----------+---------+---------------------+

是否有一个select语句可以在不编写程序逻辑的情况下返回它？

+----+----------+---------+-----------+---------+
| id | open     | assign  | complete  | close   |
+----+----------+---------+-----------+---------+
|  5 |    0     |    5    |    10     |   22    |
|  6 |    0     |    7    |           |         |
+----+----------+---------+-----------+---------+

Answer 1

SELECT id,
SUM(CASE WHEN event='open' THEN seconds ELSE 0 END) as open,
SUM(CASE WHEN event='assign' THEN seconds ELSE 0 END) as assign,
SUM(CASE WHEN event='complete' THEN seconds ELSE 0 END) as complete,
SUM(CASE WHEN event='close' THEN seconds ELSE 0 END) as close
FROM t
GROUP BY id

我假设你需要每个id的秒数，它可以是max，min等。

Answer 2

这是将行转换为列，我们可以进行基于CASE的聚合

SQL Fiddle

SELECT id, 
       MAX( case when event ='open' then seconds end ) as open,
       MAX( case when event ='assign' then seconds end ) as assign,
       MAX( case when event ='complete' then seconds end ) as complete,
       MAX( case when event ='close' then seconds end ) as close
FROM Table1
GROUP BY id

MySQL选择生成新列

2 个答案: