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Hello World
作品采用:
《
署名-非商业性使用-相同方式共享 4.0 国际 (CC BY-NC-SA 4.0)
》许可协议授权
持续更新......
USE test01;
ALTER TABLE `user` ADD CONSTRAINT pk_id PRIMARY KEY(`id`);
ALTER TABLE `person1` DROP PRIMARY KEY;
ALTER TABLE `person1` ADD PRIMARY KEY (`uid`,`pid`);
alter table 从表 add [constraint] 外键名称 foreign key (从表外键字段名) references 主表(主表的主键);
ALTER TABLE `userInfo` ADD CONSTRAINT userInfo_user_fk FOREIGN KEY(`id`) REFERENCES `user`(`id`);
ALTER TABLE `userInfo` DROP FOREIGN KEY userInfo_user_fk;
CREATE TABLE person1(
`uid` CHAR(12) NOT NULL,
`pid` CHAR(12) NOT NULL,
`text` CHAR(50)
);
INSERT INTO user1(NO,NAME) VALUE ("125","achong");
INSERT INTO user1(NO,NAME) VALUE ("125","achong1"),("126","achong2"),("127","achong3");
INSERT INTO
userInfo(id, address, phone)
VALUE
("125","广东省清远市111",10001),
("126","广东省清远市222","10002"),
("127","广东省清远市333","10003");
ALTER TABLE user1 ADD `phone`CHAR(11);
create database userdb;
DROP TABLE user22;
DELETE FROM person1 WHERE `text`= "qwe00";
对比delete,truncate table的执行熟读更快,使用的系统资源和事务日志资源更少,并且删除数据后的标识列会重新开始编号。
truncate table t_user;
ALTER TABLE `user1` RENAME `user`;
ALTER TABLE user1 CHANGE `phone` `sex`CHAR(1);
update dept set loc='SH' where deptno=30;
SHOW DATABASES;
SHOW TABLES;
DESC `userInfo`;
SELECT * FROM `userInfo`;
SELECT * FROM `person1`;
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