mysql - 在 'case function' 子句中使用 'ON'

Question

我需要加入三张 table 。

Table1 具有 id、Name、idObject、lineItem 列。Table2 包含列 id、City、idLineItem、idOrder、idSupplier、idAdv。Table3 有 idAdv、State 列。

我的查询是:

select Table1.id, Table1.Name, Table1.idObject, Table2.City, Table3.State
from Table1 
join Table2 ON case 
                 when Table1.Name='abc' then Table1.idObject=Table2.idLineItem
                 when Table1.Name='def' then Table1.idObject=Table2.idOrder
                 else Table1.idObject=Table2.idSupplier
               end
join Table3 on Table2.idAdv=Table3.idAdv
group by Table1.id, Table1.idObject;

Answer 1

CASE 语句只能返回单个值，因此您必须将比较移到 CASE 之外。像这样的事情:

select Table1.id, Table1.Name, Table1.idObject, Table2.City, Table3.State
from Table1 
join Table2 ON Table1.idObject = case 
                 when Table1.Name='abc' then Table2.idLineItem
                 when Table1.Name='def' then Table2.idOrder
                 else Table2.idSupplier
               end
join Table3 on Table2.idAdv=Table3.idAdv
group by Table1.id, Table1.idObject;