在SELECT子句中的列之间使用相等性检查

Question

我正在使用Microsoft SQL Server 2012,我想运行这个看似简单的查询:

SELECT 
    FirstEvent.id AS firstEventID, 
    SecondEvent.id AS secondEventID, 
    DATEDIFF(second, FirstEvent.WndFGEnd, SecondEvent.WndFGStart) AS gap, 
    FirstEvent.TitleID = SecondEvent.TitleID AS titlesSameCheck
FROM VibeFGEvents AS FirstEvent
RIGHT OUTER JOIN VibeFGEvents AS SecondEvent
ON 
    FirstEvent.intervalMode = SecondEvent.intervalMode 
    AND FirstEvent.id = SecondEvent.id - 1 
    AND FirstEvent.logID = SecondEvent.logID

但是FirstEvent.TitleID = SecondEvent.TitleID AS titlesSameCheck在SELECT子句中语法不正确.但SELECT子句(Transact-SQL)文档包含以下语法:

SELECT [ ALL | DISTINCT ]
[ TOP ( expression ) [ PERCENT ] [ WITH TIES ] ] 
<select_list> 
<select_list> ::= 
    { 
        * 
        | { table_name | view_name | table_alias }.* 
        | {
            [ { table_name | view_name | table_alias }. ]
                { column_name | $IDENTITY | $ROWGUID } 
            | udt_column_name [ { . | :: } { { property_name | field_name } 
            | method_name ( argument [ ,...n] ) } ]
            | expression
            [ [ AS ] column_alias ] 
            }
        | column_alias = expression 
    } [ ,...n ]

我认为这意味着表达式在select子句中是有效的,实际上给出的例子包括类似的东西1 + 2.看着为表现形式的文档:

{ constant | scalar_function | [ table_name. ] column | variable 
    | ( expression ) | ( scalar_subquery ) 
    | { unary_operator } expression 
    | expression { binary_operator } expression 
    | ranking_windowed_function | aggregate_windowed_function
}

布尔等式检查是有效的表达式,实际上=(等于)(Transact-SQL)文档中给出的示例表达式包括一个:

SELECT DepartmentID, Name
FROM HumanResources.Department
WHERE GroupName = 'Manufacturing'

虽然在WHERE条款中没有该SELECT条款.看起来我不能使用=等于运算符来比较我的SELECT子句中的表达式,因为它们被错误地解释为赋值.

如何FirstEvent.TitleID = SecondEvent.TitleID AS titlesSameCheck在my SELECT子句中包含等效的布尔相等列比较？

Answer 1

像这样:

case when FirstEvent.TitleID = SecondEvent.TitleID then 1 else 0 end as titlesSameCheck 

Answer 2

您不能直接使用布尔类型,条件语句除外(case,where,having等)

解决问题的最佳方法是做类似的事情

select case when x = y then 'true' else 'false' end

该bit类型可能最接近布尔值.

select CAST(case when x = y then 1 else 0 end as bit)

当然,使用最能代表你所追求的两个值.