仅对一列使用WHERE子句

如果你愿意 流浪者和宠物分开,然后可以使用聚合:

SELECT (CASE WHEN d.owner IS NULL THEN 'stray' ELSE 'pet' END) as status,
       COUNT(*) as dogs_count, SUM(d.age) AS total_age
FROM dogs d
WHERE d.owner IS NULL
GROUP BY status;

还可以使用条件聚合将所有值放在一行中:

SELECT COUNT(*) as dogs_count, SUM(d.age) AS total_age,
       SUM(d.owner IS NULL) as num_strays,
       SUM(CASE WHEN d.owner IS NULL THEN d.age ELSE 0 END) as strays_age
FROM dogs d

select count(*) as Total_Dogs, sum(d.owner IS NOT NULL) as dogs_count, 
       sum(d.age) as total_age
from dog d;