你如何从 sql 语句返回一个常量？
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How do you return a constant from an sql statement?
提问by wusher
How do I return a constant from an sql statement?
如何从 sql 语句返回常量？
For example how would I change the code below so "my message" would return if my (boolean expression) was true
例如，如果我的（布尔表达式）为真，我将如何更改下面的代码，以便“我的消息”返回
if (my boolean expression)
"my message"
else
select top 1 name from people;
I am using ms sql 2000
我正在使用 ms sql 2000
回答by Ned Batchelder
Did you try:
你试过了吗：
select 'my message';
回答by Kon
select "my message" as message
回答by Vinko Vrsalovic
I don't have MSSQL handy, but check the syntax for the CASE statement in case I got it wrong and also I'm not sure if the TOP 1 should go outside the case as I put it here or if it should go inside (ELSE TOP 1 name). The idea is:
我手边没有 MSSQL，但请检查 CASE 语句的语法，以防万一我弄错了，而且我不确定 TOP 1 是否应该在我放在这里的情况下放在案例之外，或者是否应该放在里面（其他 TOP 1 名称）。这个想法是：
SELECT TOP 1 CASE WHEN myexpression = 'true' THEN 'my message' ELSE name END
FROM people;
Here myexpression has to be either constants or related to the tables present in the query, for example
这里 myexpression 必须是常量或与查询中存在的表相关，例如
CASE WHEN address LIKE '%Michigan%'
where address is another field in the table people.
其中地址是表 people 中的另一个字段。
PS: Found the MSSQL CASE syntax here:-)
PS：在这里找到了 MSSQL CASE 语法:-)
回答by user35559
I just tried this on the AdventureWorks database and it works
我刚刚在 AdventureWorks 数据库上试过这个，它工作正常
Use AdventureWorks
Declare @myVar int
SET @myVar = 1
if (@myVar = 2)
select top 2 * from HumanResources.Department
else
select top 1 * from HumanResources.Department
回答by Bert
select top 1 name
from people
where @MyParameter = whatever
union
select 'my message' as name
where @MyParameter != whatever
All in one statement.
全在一份声明中。
