假设我们有一个表:
键 | 值 | _count | |
---|---|---|---|
a | b | 3 | |
c | d | <2>
您可以将cross join
与left join
一起用于较短的解决方案:
select t1.key, t2.value, coalesce(t3._count, 0) from tbl t1
cross join tbl t2 left join tbl t3 on t1.key = t3.key and t2.value = t3.value;