下面的两种说法是等价的吗?
SELECT [...]
FROM [...]
WHERE some_col in (1,2,3,4,5) AND some_other_expr
和
SELECT [...]
FROM [...]
WHERE some_col in (1,2,3) or some_col in (4,5) AND some_other_expr
有什么真值表可以用来验证吗?
下面的两种说法是等价的吗?
SELECT [...]
FROM [...]
WHERE some_col in (1,2,3,4,5) AND some_other_expr
和
SELECT [...]
FROM [...]
WHERE some_col in (1,2,3) or some_col in (4,5) AND some_other_expr
有什么真值表可以用来验证吗?
And
优先于Or
,所以即使a <=> a1 Or a2
Where a And b
不一样
Where a1 Or a2 And b,
因为那会被当作
Where a1 Or (a2 And b)
为了使它们保持一致,您需要以下内容(使用括号覆盖优先规则):
Where (a1 Or a2) And b
下面是一个例子来说明:
Declare @x tinyInt = 1
Declare @y tinyInt = 0
Declare @z tinyInt = 0
Select Case When @x=1 OR @y=1 And @z=1 Then 'T' Else 'F' End -- outputs T
Select Case When (@x=1 OR @y=1) And @z=1 Then 'T' Else 'F' End -- outputs F
对于那些喜欢查阅参考资料的人(按字母顺序):