添加唯一 约束,只能是唯一的
CREATE TABLE user(
ID CHAR(16) PRIMARY KEY NOT NULL,
NICK CHAR(10),
EMAIL CHAR(50) NOT NULL UNIQUE,
FIRSTNAME CHAR(10),
LASTNAME CHAR(10)
# UNIQUE(EMAIL) 这么添加也可以
)
添加约束性别是 ‘男’ Or ‘女’
ALTER TABLE `user`
ADD SEX CHAR(2) NULL CHECK(SEX = '男' Or SEX = '女')
CONCAT字符串拼接
CONCAT(u.NICK,’-都我的’) AS 店主
SELECT u.ID,CONCAT(u.NICK,'-都我的') AS 店主,s.NAME FROM `user` u JOIN store s
ON u.ID = s.OWNER
#GROUP BY u.ID
ORDER BY u.ID
随机数
RAND()
数字转字符串,字符串截取
RIGHT(cast(RAND() AS char(16)),14) AS 随机ID
#Or
(SUBSTRING(cast(RAND() AS char(18)),3,16))
#查询user有几个store(关闭MYSQL严格模式,严格模式不会用,待加强)
SELECT
u.ID,u.NICK ,
COUNT(*) AS 拥有store数量
FROM `user` u JOIN store s
ON u.ID = s.OWNER
GROUP BY s.OWNER
修改product table column ID 为 default random string
ALTER TABLE product
MODIFY COLUMN ID CHAR(16) NOT NULL DEFAULT (SUBSTRING(cast(RAND() AS char(18)),3,16))
更新ID为‘4’的元组NAME属性在store表中
UPDATE store
set NAME = '阳光八百超市'
WHERE ID = '4'