mysql基础

mysql的条件判断

SELECT
`产品号码`,
`产品名称`,
`产品单价`,
CASE
WHEN `产品单价`<(SELECT AVG(`产品单价`) FROM `产品信息`) THEN 1
WHEN `产品单价`>=2*(SELECT AVG(`产品单价`) FROM `产品信息`) THEN 2
ELSE 3
END AS `顾客级别`
FROM `产品信息`;

mysql 的过滤disinct

select disinct * from lala

mysql 的 having

having在mysql后执行
写在group by 后