查询计数值减去的SQL

Question

我有一个数据库。包含几个表，有一个表名

  

stockdiary

，有一个字段

  

单元

示例：

**units**
-3
7
-8
-2
20

有负值和正值，如何查询仅对负值求和

Answer 1

SELECT SUM(units) 
FROM stockdiary
WHERE units < 0

Answer 2

SELECT SUM(CASE WHEN units<0 THEN units ELSE 0 END) as NegativeTotal 
from stockdiary

OR

SELECT SUM(units) as NegativeTotal 
    from stockdiary where units<0