[英]Use comparison signs inside a sql case statement
I'm looking for a way to build case statements in a sql select query using less than and greater than signs. 我正在寻找一种使用小于和大于符号在sql select查询中构建case语句的方法。 For example, I want to select a ranking based on a variable: 例如,我想根据变量选择排名:
DECLARE @a INT
SET @a = 0
SELECT CASE
WHEN @a < 3 THEN 0
WHEN @a = 3 THEN 1
WHEN @a > 3 THEN 2
END
I'd like to write it as: 我想把它写成:
DECLARE @a INT
SET @a = 0
SELECT CASE @a
WHEN < 3 THEN 0
WHEN 3 THEN 1
WHEN > 3 THEN 2
END
...but SQL doesn't let me use the < and > signs in this way. ...但SQL不允许我以这种方式使用<和>符号。 Is there a way that I can do this is SQL 2005, or do I need to use the code like in the first one. 有没有办法可以做到这一点是SQL 2005,还是我需要像第一个那样使用代码。
The reason for only wanting the code there once is because it would make the code a lot more readable/maintainable and also because I'm not sure if SQL server will have to run the calculation for each CASE statement. 只需要一次代码的原因是因为它会使代码更易读/可维护,而且因为我不确定SQL服务器是否必须为每个CASE语句运行计算。
I'm looking for a VB.NET case statement equivelent: 我正在寻找一个VB.NET案例声明equivelent:
Select Case i
Case Is < 100
p = 1
Case Is >= 100
p = 2
End Select
Maybe it's not possible in SQL and that's ok, I just want to confirm that. 也许这在SQL中是不可能的,没关系,我只想确认一下。
You can use the SIGN function as 您可以使用SIGN功能
DECLARE @a INT
SET @a = 0
SELECT CASE SIGN(@a - 3)
WHEN -1 THEN 0
WHEN 0 THEN 1
WHEN 1 THEN 2
END
If @a
is smaller than 3, then @a - 3
results in a negative int, in which SIGN returns -1. 如果@a
小于3,则@a - 3
导致负int,其中SIGN返回-1。
If @a
is 3 or greater, then SIGN returns 0 or 1, respectively. 如果@a
为3或更大,则SIGN分别返回0或1。
If the output you want is 0, 1 and 2, then you can simplify even more: 如果您想要的输出是0,1和2,那么您可以进一步简化:
DECLARE @a INT
SET @a = 0
SELECT SIGN(@a - 3) + 1
Using SIGN
as suggested by @Jose Rui Santos seems a nice workaround. 使用@Jose Rui Santos建议的 SIGN
似乎是一个很好的解决方法。 An alternative could be to assign the expression an alias, use a subselect and test the expression (using its alias) in the outer select: 另一种方法是为表达式分配别名,使用子选择并在外部选择中测试表达式(使用其别名):
SELECT
…,
CASE
WHEN expr < 3 THEN …
WHEN expr > 3 THEN …
END AS …
FROM (
SELECT
…,
a complex expression AS expr
FROM …
…
)
SELECT
CASE
WHEN ColumnName >=1 and ColumnName <=1 THEN 'Fail'
WHEN ColumnName >=6 THEN 'Pass'
ELSE 'Test'
END
FROM TableName
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