Question

我有两个表，即表1 和表2
表1

custId--custName--custAge
c1--c1name--32  
c2--c2name--41  
c3--c3name--41

表2

custId--verified--custName  
c1--Y--c1FullName  
c2--N--c2FullName

我需要加入Table1和Table2，因此如果表2中的验证列为Y，我需要Table2中的custName而不是Table1。
因此，所需的输出为：（覆盖表2中的custName列，如果验证列为该custId的Y ）

custId--custName--custAge  
c1--c1FullName--32  
c2--c2name--41  
c3--c3name--41

我写了以下查询，但没有给出正确的结果。请帮忙。

select T1.custId, NVL(T2.custName, T1.custName),T1.custAge   
from Table1 T1  
left join Table2 T2 on T1.custId=T2.custId and T2.verified='Y'

Answer 1

您可以使用CASE语句来实现此目的：

SELECT      tab1.custId,
            CASE
                WHEN (tab2.verified = 'Y')
                THEN tab2.custName
                ELSE tab1.custName
            END AS CustName,
            tab1.custAge

FROM        Table1 tab1
LEFT JOIN   Table2 tab2 ON tab1.custId = tab2.custId

在此处查看 - ＆gt; http://rextester.com/EVOMK25746（这个小提琴基于 SQL Server 构建，但是，该查询也可以在 Oracle 数据库上运行< / em>的）

希望这有帮助!!!

Answer 2

尝试此查询一次..

select * into #tab1 from
(
select 'c1' custId,'c1name' custName,31 custAge
union all
select 'c2' ,'c2name' ,41 
union all
select 'c3' ,'c3name' ,41 

) as a

select * into #tab2 from
(
select 'c1' custId,'Y'verified,'c1FullName' custName
UNION ALL
SELECT 'c2','N','c2FullName '
) as a

SELECT T1.custId,CASE WHEN T2.verified='Y' THEN T2.custName ELSE T1.custName END AS CUSTNAME,T1.custAge FROM #tab1 T1
LEFT JOIN #tab2 T2 ON T1.custId=T2.custId

Answer 3

select custId, custName, custAge
  from Table1
       natural join
       ( select custId 
           from Table2
          where verified='N' ) t2
union
select custId, custName, custAge
  from ( select custId, custAge from Table1 ) t1
       natural join
       ( select custId, custName
           from Table2
          where verified='Y' ) t2;

SQL连接覆盖左表的特定列

3 个答案: