SQL 加入以覆盖左侧的特定列 table

Question

我有两个 table，即 Table1 和 Table2
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，这样如果在 table 2 中验证的列是 Y，我需要来自 Table2 而不是 Table1 的 custName。
因此，所需的输出是：（如果该 custId 的已验证列为 Y，则覆盖 Table2 中的 custName 列）

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：

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 -> http://rextester.com/EVOMK25746（此 fiddle 构建于 SQL Server ，但是，查询也应该在 Oracle 数据库上工作)

希望对您有所帮助！！！

Answer 2

尝试这个查询一次..

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 加入以覆盖左侧的特定列 table

SQL join to override particular column of left table

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sql-server

oracle

rdbms

join