Question

有两张表，是主子表关系，我要查询出 主表的总记录数和子表总记录数，一条sql语句

Answer 1

主外键关联跟记录数没啥关系啊。除非你业务上有什么逻辑，要不无异于一条语句差两张无关表的记录数。倒是可以不做关联的情况下分别count两张表的一个字段，但是会非常非常慢啊～不知道什么限制你非要用一条sql，要是分别count会快很多啊。

select count(*) from table_a
union
select count(*) from table_b
这样倒是一条语句，不过我觉得你要的应该不是这个吧？

这样可以，刚想起来select (select count(*) from table_a) as A ,(select count(*) from table_b) as B from dual

Answer 2

用子查询
select (select count(*) from table_a) as A ,(select count(*) from table_b) as B from dual

Answer 3

select (select count(*) from table_a) as A ,(select count(*) from table_b) as B from dual

Answer 4

select cnt_p,cnt_c
from
(select count(1)cnt_p from父表) a,
(select count(1) cnt_c from 子表) b

Answer 5

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