我想使用 CASE 语句更新 sql server 2005 中的一些记录
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I want to use CASE statement to update some records in sql server 2005
提问by user2236361
UPDATE dbo.TestStudents
SET LASTNAME =
( CASE
WHEN (LASTNAME = 'AAA') THEN 'BBB'
WHEN (LASTNAME = 'CCC') THEN 'DDD'
WHEN (LASTNAME = 'EEE') THEN 'FFF'
ELSE (LASTNAME)
END )
The statement work for the purpose but the else condition scan through every record in the table. Is there any way I can leave the unaffected rows as they are?
该语句用于此目的，但 else 条件会扫描表中的每条记录。有什么办法可以让不受影响的行保持原样吗？
回答by John Woo
Add a WHEREclause
添加WHERE条款
UPDATE dbo.TestStudents
SET LASTNAME = CASE
WHEN LASTNAME = 'AAA' THEN 'BBB'
WHEN LASTNAME = 'CCC' THEN 'DDD'
WHEN LASTNAME = 'EEE' THEN 'FFF'
ELSE LASTNAME
END
WHERE LASTNAME IN ('AAA', 'CCC', 'EEE')
回答by David
This is also an alternate use of case-when...
这也是 case-when 的另一种用法...
UPDATE [dbo].[JobTemplates]
SET [CycleId] =
CASE [Id]
WHEN 1376 THEN 44 --ACE1 FX1
WHEN 1385 THEN 44 --ACE1 FX2
WHEN 1574 THEN 43 --ACE1 ELEM1
WHEN 1576 THEN 43 --ACE1 ELEM2
WHEN 1581 THEN 41 --ACE1 FS1
WHEN 1585 THEN 42 --ACE1 HS1
WHEN 1588 THEN 43 --ACE1 RS1
WHEN 1589 THEN 44 --ACE1 RM1
WHEN 1590 THEN 43 --ACE1 ELEM3
WHEN 1591 THEN 43 --ACE1 ELEM4
WHEN 1595 THEN 44 --ACE1 SSTn
ELSE 0
END
WHERE
[Id] IN (1376,1385,1574,1576,1581,1585,1588,1589,1590,1591,1595)
I like the use of the temporary tables in cases where duplicate values are not permitted and your update may create them. For example:
我喜欢在不允许重复值并且您的更新可能会创建它们的情况下使用临时表。例如：
SELECT
[Id]
,[QueueId]
,[BaseDimensionId]
,[ElastomerTypeId]
,CASE [CycleId]
WHEN 29 THEN 44
WHEN 30 THEN 43
WHEN 31 THEN 43
WHEN 101 THEN 41
WHEN 102 THEN 43
WHEN 116 THEN 42
WHEN 120 THEN 44
WHEN 127 THEN 44
WHEN 129 THEN 44
ELSE 0
END AS [CycleId]
INTO
##ACE1_PQPANominals_1
FROM
[dbo].[ProductionQueueProcessAutoclaveNominals]
WHERE
[QueueId] = 3
ORDER BY
[BaseDimensionId], [ElastomerTypeId], [Id];
---- (403 row(s) affected)
UPDATE [dbo].[ProductionQueueProcessAutoclaveNominals]
SET
[CycleId] = X.[CycleId]
FROM
[dbo].[ProductionQueueProcessAutoclaveNominals]
INNER JOIN
(
SELECT
MIN([Id]) AS [Id],[QueueId],[BaseDimensionId],[ElastomerTypeId],[CycleId]
FROM
##ACE1_PQPANominals_1
GROUP BY
[QueueId],[BaseDimensionId],[ElastomerTypeId],[CycleId]
) AS X
ON
[dbo].[ProductionQueueProcessAutoclaveNominals].[Id] = X.[Id];
----(375 row(s) affected)
回答by Damien_The_Unbeliever
If you don't want to repeat the list twice (as per @J W's answer), then put the updates in a table variable and use a JOINin the UPDATE:
如果您不想重复该列表两次（根据@JW 的回答），则将更新放在表变量中并JOIN在以下内容中使用 a UPDATE：
declare @ToDo table (FromName varchar(10), ToName varchar(10))
insert into @ToDo(FromName,ToName) values
('AAA','BBB'),
('CCC','DDD'),
('EEE','FFF')
update ts set LastName = ToName
from dbo.TestStudents ts
inner join
@ToDo t
on
ts.LastName = t.FromName
