Question

HELO，我试图从表wp_formmaker_submits转置一个名为element_label的列。

原始表是

+---------+---------------+------------------+----------+
| FORM_ID | ELEMENT_LABEL |    ELEMENT_VALUE | GROUP_ID |
+---------+---------------+------------------+----------+
|      10 |             1 |       18-11-2014 |        1 |
|      10 |             2 |         Logistic |        1 |
|      10 |             3 | Warehouse Supply |        1 |
|      10 |             4 |              Red |        1 |
|      10 |             1 |       19-11-2014 |        2 |
|      10 |             2 |   Transportation |        2 |
|      10 |             3 |          Vehicle |        2 |
|      10 |             4 |            Green |        2 |
+---------+---------------+------------------+----------+

我正在使用此查询

SELECT 
CASE WHEN element_label = 1 THEN element_value END a1,
CASE WHEN element_label = 2 THEN element_value END a2,
CASE WHEN element_label = 3 THEN element_value END a3,
CASE WHEN element_label = 4 THEN element_value END a4
FROM wp_formmaker_submits

我的结果是

+------------+----------------+------------------+--------+
|         A1 |             A2 |               A3 |     A4 |
+------------+----------------+------------------+--------+
| 18-11-2014 |           NULL |             NULL |   NULL |
|       NULL |       Logistic |             NULL |   NULL |
|       NULL |           NULL | Warehouse Supply |   NULL |
|       NULL |           NULL |             NULL |    Red |
| 19-11-2014 |           NULL |             NULL |   NULL |
|       NULL | Transportation |             NULL |   NULL |
|       NULL |           NULL |          Vehicle |   NULL |
|       NULL |           NULL |             NULL |  Green |
+------------+----------------+------------------+--------+

如何删除NULL，所以我会得到这样的结果

+---------+----------+------------+----------------+------------------+-------+
| FORM_ID | GROUP_ID |         A1 |             A2 |               A3 |    A4 |
+---------+----------+------------+----------------+------------------+-------+
|      10 |        1 | 18-11-2014 |       Logistic | Warehouse Supply |   Red |
|      10 |        2 | 19-11-2014 | Transportation |          Vehicle | Green |
+---------+----------+------------+----------------+------------------+-------+

Answer 1

添加聚合函数，例如

MAX(CASE WHEN element_label = 1 THEN element_value END) a1

Answer 2

试试这个

SELECT form_id,group_id,
MAX(CASE WHEN element_label = 1 THEN element_value END) as a1,
MAX(CASE WHEN element_label = 2 THEN element_value END) as a2,
MAX(CASE WHEN element_label = 3 THEN element_value END) as a3,
MAX(CASE WHEN element_label = 4 THEN element_value END) as a4
FROM tbl
Group by form_id,group_id

如果仍然有问题，那么plz在sqlfiddle上共享你的表模式。

MYSQL选择案例行到列

2 个答案: