SQL选择value ='X'或min值的位置

Question

我有一个庞大的客户数据库，客户表中有人和他们与组织的关系。 人们可能属于多个组织（ 这允许组织内的部门 ）。 具有多个组织的人员必须具有默认组织，这通常在isDefault = T确定，但是前端应用程序还可以通过选择MIN(RowID)来确定默认应用程序isDefault = F

因此在下表中我们知道PersonId 3的默认OrgID为11 （IsDefault = T）但是，我需要找出查找PersonID 12默认值的查询。 即

Select orgId as default from myTable
where personID = 12
and isDefault = 'T'

如果返回0行，则执行如下查询：

Select orgId as default from myTable
where personID = 12
and 
RowId in (select Min(rowId) 
from myTable 
where PersonId = 12)


RowID | PersonID  | OrgId  |  isDefault
1     |    12     |   14   |     F
2     |    12     |   17   |     F
3     |    3      |   11   |     T
4     |    3      |   14   |     F

Answer 1

我想你可以通过两次订购得到你想要的东西，首先是IsDefault是T还是F，然后是RowId，并取得最佳结果：

SELECT TOP 1 OrgId as [Default]
FROM MyTable
WHERE PersonId = 12
ORDER BY
    CASE WHEN IsDefault = 'T' THEN 0 ELSE 1 END,
    RowId

Answer 2

在MySql服务器中，您可以使用限制1进行联合：

SELECT OrgId AS `default`
FROM (
    SELECT OrgId FROM MyTable
    WHERE PersonID = 12
    and isDefault = 'T'

    UNION

    SELECT OrgId FROM MyTable
    WHERE PersonId = 12
    AND RowId in (
        SELECT MIN(RowId)
        FROM MyTable
        WHERE PersonId = 12
    )
) SomeName LIMIT 1;

对于SQL Server：

SELECT TOP 1 OrgId AS [default]
FROM (
    SELECT OrgId FROM MyTable
    WHERE PersonID = 12
    and isDefault = 'T'

    UNION

    SELECT OrgId FROM MyTable
    WHERE PersonId = 12
    AND RowId in (
        SELECT MIN(RowId)
        FROM MyTable
        WHERE PersonId = 12
    )
) SomeName;

Answer 3

没试过执行这个但是期望这应该有效。 IsDefault会使子查询短路。

  Select orgId as default from myTable o
   where personID = 12 
       and  
       ( IsDefault = 'T' OR
                   RowId = (select Min(rowId)  
                               from myTable i
                             where i.PersonId = o.PersonId
                           )  
        )

Answer 4

将此逻辑放入一个查询中相当复杂。 您必须将所有结果合并在一起，跟踪结果的来源。 然后，您必须计算来自第一部分的行数，并仅保留适当结果集中的行。

select orgid, mytable
from (select t.*, sum(which) over (partition by null) as whichcnt
      from ((Select 1 as which, orgId as default
             from myTable
             where personID = 12 and
                   isDefault = 'T'
            )
            union all
           (Select 0 as which, orgId as default
            from myTable
            where personID = 12 and 
                  RowId in (select Min(rowId) from myTable where PersonId = 12)
           )
          ) t
     ) t
where whichcnt > 0 and which = 1 or whichcnt = 0

如果您可以使用TSQL而不是单个查询，那么您可以只运行第一个版本，检查结果中的行数，然后确定要采用的结果集。

Answer 5

请试试这个

select PersonID ,OrgID from mytable where isDefault='T'
union all

select personID,min(OrgID) [default]
from myTable P
where  not exists 
(select * from mytable C where P.PersonID=C.PersonID and C.isDefault='T')
group by personID

Answer 6

这取决于表的大小是什么索引。如果说rowid有唯一的聚簇索引和personid，并且isdefault有一个nc索引我将使用两个statemnts。

 declare @orgid int = null
 select @orgid =orgid from table where personid = 12 and isdefault = 'T'
 if (orgid  is null)
 begin
 select @orgid = orgid 
 from mytable
 where rowid = (
 select min(rowid)from table where personid = 12 and isdefault = 'F'
 )
 end