sql查询在一个case-when列上联接多个表

我的sql是这样的：

select case when.....end as colA, table2.col3
from table1
join table2 on table2.colB = colA

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在when语句的情况下，还有其他一些表列，这是否可行？我错误地说colA无效。

where或on子句中不理解列别名

您可以通过子查询执行此操作，假设案例仅涉及表1中的列：

否则，您可以将case语句放在on子句中：

select case when.....end as colA, t2.col3
from (select table1.*, (case when.....end) as colA
      from table1
     ) t1 join
     table2 t2
     on t2.colB = t1.colA;

select case when.....end as colA, t2.col3
from (select table1.*, (case when.....end) as colA
      from table1
     ) t1 join
     table2 t2
     on t2.colB = ( case when.....end );