1.逻辑运算

and 、or 、 not

SELECT id, sales_a, sales_b, (( sales_a > 15 ) AND ( sales_b > 15 )) AS "双优", (( sales_a > 15 ) 
OR ( sales_b > 15 )) AS "单优" 
FROM
    chapter7

result:

2.数学运算

常见的数学运算包括三角函数、指数运算、对数运算、取整运算(向上取整和向下取整)等。这里选取几个常用的进行说明

2.1 abs()求绝对值

SELECT
id,
sales_a,
sales_b,
(sales_a - sales_b) as "差值",
ABS(sales_a - sales_b) as "绝对差值"
FROM
chapter7

2.2 向上取整

SELECT CEIL(2.9)

result:

2.3 向下取整

SELECT FLOOR(2.9)

result:

2.4 随机数生成

SELECT id, RAND() as "随机数" FROM chapter7

result:

2.5 小数保留指定位数

SELECT ROUND(1.234, 2) 

result:

这里是对1.234保留2位小数

2.6 正负判断

SELECT
id,
sales_a,
sales_b,
(sales_a - sales_b) as "差值",
SIGN(sales_a - sales_b) as "正负"
FROM
chapter7

result:

这里是对sales_a列和sales_b列的差值进行判断正负。如果差值为正，则结果为1；结果为负，结果为-1；差值为0，结果为0