获取一个BIT列MAX值

Question

我有一个SELECT请求“内连接”在连接表是位类型的柱。

我要选择1，如果连接表是用1最多一个值。如果它不是值为0的情况。

所以，如果我有：

PERSID | NAME
1      |  Toto
2      |  Titi
3      |  Tata

而第二个表

PERSID | BOOL
1      |  0
1      |  0
2      |  0
2      |  1

我想有结果

Toto -> 0
Titi -> 1
Tata -> 0

我试试这个：

SELECT 
     sur.*
    ,MAX(bo.BOOL)    

    FROM SURNAME sur              
    INNER JOIN BOOL bo
    ON bo.IDPERS = sur.IDPERS

但是MAX不适用于BIT列..所以，我该怎么办呢？

谢谢，

Answer 1

你可以将其转换为INT，甚至将它转换回一个BIT如果您需要

SELECT 
     sur.*
    ,CAST(MAX(CAST(bo.BOOL as INT)) AS BIT)
    FROM SURNAME sur              
    INNER JOIN BOOL bo
    ON bo.IDPERS = sur.IDPERS

Answer 2

尝试：

max(cast(bo.BOOL as int))

Answer 3

单程

SELECT 
     sur.*
    ,MAX(convert(tinyint,bo.BOOL))    

    FROM SURNAME sur              
    INNER JOIN BOOL bo
    ON bo.IDPERS = sur.IDPERS

Answer 4

您可以通过强制隐式转换避免凌乱寻找双投：

SELECT 
     sur.*
    ,CAST(MAX(1 * bo.BOOL) AS BIT)
    FROM SURNAME sur              
    INNER JOIN BOOL bo
    ON bo.IDPERS = sur.IDPERS

Answer 5

如果你想只有那些恰好与一个设置位：

declare @Surname as Table ( PersId Int, Name VarChar(10) )
insert into @Surname ( PersId, Name ) values
  ( 1, 'Toto' ), ( 2, 'Titi' ), ( 3, 'Tata' ), ( 4, 'Tutu' )

declare @Bool as Table ( PersId Int, Bool Bit )
insert into @Bool ( PersId, Bool ) values
  ( 1, 0 ), ( 1, 0 ),
  ( 2, 0 ), ( 2, 1 ),
  ( 4, 1 ), ( 4, 0 ), ( 4, 1 )

select Sur.PersId, Sur.Name, Sum( Cast( Bo.Bool as Int ) ) as [Sum],
  case Sum( Cast( Bo.Bool as Int ) )
    when 1 then 1
    else 0
    end as [Only One]
  from @Surname as Sur left outer join
    @Bool as Bo on Bo.PersId = Sur.PersId
  group by Sur.PersId, Sur.Name
  order by Sur.Name