两个子查询间运算有没有简便方法？

[Mac]

select (select sum(cost) from a where id=xxx) ys, (select sum(cost) from b where id=xxx) yf, ys-yf from abc

我这么写貌似是错的，必须再写一遍两个子查询用减号相连么？

[petelin]

可以考虑 join

[delavior]

必须再嵌套一层，定义的别名在同一个 select 里肯定是无效的

[petelin]

`select a.sum - a.sum from (select id,sum(in_money) as sum from A where id = 0) as a,(select id,sum(out_money) as sum from B where id = 0) as b;`

`select (select sum(in_money) from A where id = 0) - (select sum(out_money) from B where id = 0);`

[klesh]

SELECT SUM(a.cost - b.cost)
FROM a
LEFT JOIN b ON (a.id = b.id)
WHERE a.id = xxx;