SQL可以跨多个表计算聚合函数吗？

假设我有两个现有的桌子,“狗”和“猫”：

dog_name | owner
 ---------+------
 Sparky   | Bob
 Rover    | Bob
 Snoopy   | Chuck
 Odie     | Jon

 cat_name | owner
 ---------+------
 Garfield | Jon
 Muffy    | Sam
 Stupid   | Bob

如何使用此输出编写查询？

owner | num_dogs | num_cats
 ------+----------+---------
 Bob   |     2    |    1
 Chuck |     1    |    0
 Sam   |     0    |    1
 Jon   |     1    |    1

解决方法

select owner,sum(num_dogs),sum(num_cats) from
  (select owner,1 as num_dogs,0 as num_cats from dogs
   union
   select owner,0 as num_dogs,1 as num_cats from cats)
group by owner

（编辑：安卓应用网）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!