sql - IN 条件左侧的多列

Question

这是一个有效的陈述:

SELECT foo FROM table1 WHERE
  column1 IN (SELECT bar FROM table2) AND
  column2 IN (SELECT bar FROM table2)

但有没有什么办法可以避免重复SELECT bar FROM table2语句，使它更简单、更经济？

我的意思是这样的:

SELECT foo FROM table1 WHERE
  «column1 and also column2» IN (SELECT bar FROM table2)

Answer 1

您可以使用带有 EXISTS 运算符的相关子查询

select *
from table1 t1
where exists (select *
              from table2 t2
              where t2.bar in (t1.column1, t1.column2));

如果两列都应与 table2.bar 中的值匹配，则可以使用以下内容:

select *
from table1 t1
where exists (select *
              from table2 t2
              where t2.bar = t1.column1
                and t2.bar = t1.column2);