任何人都可以简化这个mysql查询

Question

任何人都可以简化这个MYSQL查询

同一个表我想用1种类型的值减去另一种类型的值

ex：sum( type1 ) - sum (type 2)

SELECT (SELECT sum(exp_amount) FROM `expenses` WHERE `account_id`  = 1 && `type_id` = 2)
     - (SELECT sum(exp_amount) FROM `expenses` WHERE `account_id`  = 1 && `type_id` = 1) AS balance FROM  `expenses` 
LIMIT 0 , 1

指导我如何在Cake php中处理此查询注意：不直接使用此查询 - ＆gt;查询（...）

Answer 1

通过使用

下面的基于案例的聚合，您可以通过单次扫描得到平衡

SELECT Coalesce(sum(CASE WHEN type_id=2 THEN exp_amount END), 0) - Coalesce(sum(CASE WHEN type_id =1 THEN exp_amount END),0) AS balance
FROM expenses
WHERE account_id = 1
  AND type_id IN (1,2)