Question

我有两张桌子：表1：id1，field1，field2，field3 表2：id2，field1，field3

我需要的是：

"select id2 from table2 where field1 = x and field3 = y;"

如果它返回空，则执行并处理以下结果：

"select field2 from table1 where field1 = x and field3 = y;"

有没有办法在SQLite的单个查询中执行此操作？

Answer 1

假设这些表可以在field1和field3上加入，那么这样的东西应该可以使用（警告：未经测试）：

select
  case when sum(count_id2)>0 then a.id2
  else b.field2 end as column
from(
  select id2,count(1) as count_id2
  from table2
  where field1=x and field3=y
  group by id2
)a
join(
  select id2,field2
  from table1
  join table2
  using(field1,field3)
  where field1=x and field3=y
)b
using(id2);

SQL动态排除，压缩成一个查询（SQLite）

1 个答案: