if if条件在sql中

Question

我想编写一个sql查询:

if此查询(select X from table1 where x = 'value1')有结果返回1 else if (select x from table2 where x = 'value2')有任何结果返回2否则返回0.

谢谢

Answer 1

一种方法是select和case:

select (case when exists (select X from table1 where x = 'value1')
             then 1
             when exists (select x from table2 where x = 'value2')
             then 2
             else 0
        end) as flag