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
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
