Question

我有以下问题。我正在尝试加入三个表：

TableA：Record_id，Reference_id，Param

表B：Doc_id，NameB

TableC：Doc_id，NameC

取决于TableA.Param中的值，我需要通过加入Reference_id来选择表B或C中的Name

我试过使用“case”约束，但没有解决：）

select  a.Record_id, a.Reference_id
       , case when Param = 'B' then b.NameB
              when Param = 'C' then c.NameC
from TableA as a inner join
     TableB as b on a.Reference_id = b.Doc_id inner join
     TableC as c on a.Reference_id = c.Doc_id

有什么想法吗？

Answer 1

您可以left join使用该条件并使用coalesce()

获取第一个非空名称

select  a.Record_id, a.Reference_id,
        coalesce(b.NameB, c.NameC) as name
from TableA as a 
left join TableB as b on a.Reference_id = b.Doc_id 
                     and Param = 'B'
                     and b.STAT = 'A'
left join TableC as c on a.Reference_id = c.Doc_id 
                     and Param = 'C'
                     and c.STAT = 'A'

BTW您的查询已关闭（错过了end）。这适用于left join s

select  a.Record_id, a.Reference_id,
        case when Param = 'B' then b.NameB
             when Param = 'C' then c.NameC
        end as name
from TableA as a 
left join TableB as b on a.Reference_id = b.Doc_id and b.STAT = 'A'
left join TableC as c on a.Reference_id = c.Doc_id and c.STAT = 'A'

Answer 2

试试这个：

SELECT a.Record_id, a.Reference_id, b.NameB AS Name
FROM TableA AS a
INNER JOIN TableB AS b ON a.Reference_id = b.Doc_id 
WHERE a.Param = 'B'

UNION

SELECT a.Record_id, a.Reference_id, c.NameC AS Name
FROM TableA AS a
INNER JOIN TableC as c ON a.Reference_id = c.Doc_id 
WHERE c.Param = 'C'

Answer 3

Ext.Inventory.prototype.addAlias = function(className,alias, update) {
    return this.addMapping(className, alias, this.aliasToName, this.nameToAliases, true);
};

使用ID T-SQL多个连接到单个列

3 个答案: