mysql - 从 A 表的一行中进行多项选择，并将结果作为多行插入 B 表中，并在一个查询中重复

Question

我需要将静态表中的数据插入到具有多个自定义选项的表中，因此如下所示。

一个表:

+------+------+--------+-------+
| name | type | weight | color |
+------+------+--------+-------+
|   1  |    A |    10  | green |
+------+------+--------+-------+
|   2  |    B |     3  | blue  |
+------+------+--------+-------+
|   3  |    D |     9  | gold  |
+------+------+--------+-------+

期望的输出:

+------+-------------+--------------+
| name | option_name | option_value |
+------+-------------+--------------+
| 1    | type        | A            |
+------+-------------+--------------+
| 1    | weight      | 10           |
+------+-------------+--------------+
| 1    | color       | green        |
+------+-------------+--------------+
| 2    | type        | B            |
+------+-------------+--------------+
| 2    | weight      | 3            |
+------+-------------+--------------+
| 2    | color       | blue         |
+------+-------------+--------------+
| 3    | type        | D            |
+------+-------------+--------------+
| 3    | weight      | 9            |
+------+-------------+--------------+
| 3    | color       | gold         |
+------+-------------+--------------+

这可能吗？

Answer 1

您可以使用交叉连接技巧来“反透视”这些值:

select 
    t.name,
    case x.i 
        when 1 then 'type'
        when 2 then 'weight'
        when 3 then 'color'
    end option_name,
    case x.i
        when 1 then type
        when 2 then cast(weight as char(50))
        when 3 then color
    end option_value
from your_table t
cross join (
    select 1 i union all
    select 2 i union all
    select 3 i
) x

cast(weight as char(50)) weight 是必需的，因为数据类型需要保持一致，weight(可能)是一个数字列，需要转换成字符串。

SQLFiddle