SQL Server：如何为不同的INSERT INTO语句编写CASE查询？

The question is referring to a T-SQL query.

问题是指T-SQL查询。

There are two tables:

有两个表:

Table_A:

 A_ID | Category | SomeValue .
 -----+----------+-----------.
   0  |    1     |   ...     .
   1  |    1     |   ...     .
   2  |    2     |   ...     .
   2  |    2     |   ...     .

and Table_B that should get filled by the Category condition of Table_A. Depending on the categories of Table_A I would like to write some data into column 1 OR column 2 of a second table. The other column shall remain null:

和Table_B应该由Table_A的Category条件填充。根据Table_A的类别,我想将一些数据写入第二列的第1列或第2列。另一列应保持为null:

 B_ID | cat_x    | cat_y     .
 -----+----------+-----------.
   0  | someval  |   null    . //Category was 1
   1  |  null    |  someval  . //Category was 2
   2  |  null    |  someval  . //Category was 2
   2  | someval  |   null    . //Category was 1

My input is a whole table. For every row it has to look up the goal column to write in.

我的输入是整张表。对于每一行,它必须查找目标列才能写入。

I tried to work with CASE, but I didn't got it. Here is some pseudo code that might help you to understand:

我尝试使用CASE,但我没有得到它。以下是一些可能有助于您理解的伪代码:

CASE
   WHEN Category=1
      THEN 
         INSERT INTO (B_ID,cat_x)
             SELECT (someval) //ID could get filled automatically
             FROM sometable
   WHEN Category = 2
      THEN 
         INSERT INTO (B_ID,cat_y)
             SELECT (someval) //ID could get filled automatically
             FROM sometable
END

My biggest problem I guess is how to write the syntax for the condition/when-clause.

我猜的最大问题是如何编写condition / when-clause的语法。

1 个解决方案

#1

Not quite. The case expression should be part of the `select query:

不完全的。 case表达式应该是`select查询的一部分:

INSERT INTO (B_ID, cat_x, cat_y)
        SELECT (case when a.category = 1 then someval end),
               (case when a.category = 2 then someval end)
        FROM A
        WHERE category IN (1, 2);