sql - 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，SELECT 子句中的 FirstEvent.TitleID = SecondEvent.TitleID AS TitlesSameCheck 语法不正确。但是the SELECT Clause (Transact-SQL) documentation包括以下语法:

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 子句中有效，并且实际上给出的示例包括 1 + 2 之类的内容。正在查看the documentation for expressions :

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

bool 相等检查是有效的表达式，实际上是the = (Equals) (Transact-SQL) documentation中给出的示例表达式。包括一个:

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

尽管在 WHERE 子句中，而不是在 SELECT 子句中。看起来我无法使用 = 相等运算符来比较 SELECT 子句中的表达式，因为它们被错误地解释为赋值。

如何在我的 SELECT 子句中包含相当于 FirstEvent.TitleID = SecondEvent.TitleID AStitlesSameCheck 的 bool 相等列比较？

Answer 1

像这样:

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