在单个SQL查询中交换同一表的列值

Question

我需要使用不同的键更新两行的列值.约束是我想在单个查询中执行此操作.

例如:

Coll1   Coll2
---------------
  A       1
  B       2
  C       3

应该是这样的

Coll1   Coll2
--------------
  A       3
  B       2
  C       1

Answer 1

使用case表达式:

update t
  set Coll2 = case when Coll1 = 'A' then 3 else 1 end
where Coll1 in ('A','C')

rextester演示:http://rextester.com/HUBDAP9516

收益:

+-------+-------+
| Coll1 | Coll2 |
+-------+-------+
| A     |     3 |
| B     |     2 |
| C     |     1 |
+-------+-------+

更新参数化版本:

declare @key1 char(1) = 'A';
declare @key2 char(1) = 'C';
update t
  set t.Coll2 =  x.Coll2
from t
  inner join t x
    on t.Coll1 <> x.Coll1
   and t.Coll1 in (@key1,@key2)
   and x.Coll1 in (@key1,@key2)

rextester演示:http://rextester.com/PKQSAV63963

收益:

+-------+-------+
| Coll1 | Coll2 |
+-------+-------+
| A     |     3 |
| B     |     2 |
| C     |     1 |
+-------+-------+