---
notion-id: 3b56b1e8-7a24-4511-85d8-b5b4e1fc177c
---
```sql
# 使用子查询将两个表的结果相减
SELECT (SELECT em1.salary
	FROM employees em1
	WHERE employee_id = 100) -
	(SELECT em2.salary
	FROM employees em2
	WHERE employee_id = 101) AS '减法'
FROM DUAL;

# 通过查询将先计算合计结果 然后再与另一个表的合计结果详见
SELECT  bank.`total_money` - bank.`local_money` - SUM(use_bank.`use_money`) AS '可用'
FROM bank LEFT JOIN use_bank 
ON bank.`bank_name` = use_bank.`bank_name`
WHERE bank.`bank_name` = ''
AND use_bank.`create_day` = '2023-3-8'
```