MySQl 常用——自用整理

函数

获取日期字段年份

year(CreateTime)

语法

UNION拼接语句，可实现自定义结果集。

SELECT  '无' AS name,count(1) as value FROM t_test where test = '1'
UNION
SELECT  '轻微' AS name,count(1) as value FROM t_test where test = '2'
UNION
SELECT  '中度' AS name,count(1) as value FROM t_test where test = '3'
UNION
SELECT  '重度' AS name,count(1) as value FROM t_test where test = '4'
UNION
SELECT  '高危' AS name,count(1) as value FROM t_test where test = '5'

命令

新增字段
ALTER TABLE t_user ADD COLUMN user_age int(11) DEFAULT NULL COMMENT '年龄' AFTER user_email;