Mysql表的各项操作实例

创建用户表

CREATE TABLE IF NOT EXISTS user10(

id SMALLINT UNSIGNED KEY AUTO_INCREMENT,

username VARCHAR(20) NOT NULL UNIQUE,

password CHAR(32) NOT NULL,

email VARCHAR(50) NOT NULL DEFAULT ‘382771946@qq.com’,

age TINYINT UNSIGNED DEFAULT 18,

sex ENUM(‘男’,’女’,’保密’) DEFAULT ‘保密’,

addr VARCHAR(200) NOT NULL DEFAULT ‘北京’,

salary FLOAT(6,2),

regTime INT UNSIGNED,

face CHAR(100) NOT NULL DEFAULT ‘default.jpg’

);

修改表名字

ALTER TABLE user10 RENAME TO user11;

ALTER TABLE user11 RENAME AS user10;

ALTER TABLE user10 RENAME user11;

RENAME TABLE user11 TO user10;

– 添加card 字段 CHAR(18)

ALTER TABLE user10 ADD card CHAR(18);

ALTER TABLE user10 ADD test1 VARCHAR(100) NOT NULL UNIQUE;

ALTER TABLE user10 ADD test2 VARCHAR(20) NOT NULL FIRST;

ALTER TABLE user10 ADD test3 INT NOT NULL DEFAULT 100 AFTER username;

– 选中一次表，完成多个操作

ALTER TABLE user10

ADD test4 INT NOT NULL DEFAULT 123 AFTER password,

ADD test5 FLOAT(6,2) FIRST,

ADD test6 SET(‘A’,’B’,’C’);

mysql> desc user10;
+----------+----------------------------+------+-----+------------------+----------------+
| Field    | Type                       | Null | Key | Default          | Extra          |
+----------+----------------------------+------+-----+------------------+----------------+
| test5    | float(6,2)                 | YES  |     | NULL             |                |
| test2    | varchar(20)                | NO   |     | NULL             |                |
| id       | smallint(5) unsigned       | NO   | PRI | NULL             | auto_increment |
| username | varchar(20)                | NO   | UNI | NULL             |                |
| test3    | int(11)                    | NO   |     | 100              |                |
| password | char(32)                   | NO   |     | NULL             |                |
| test4    | int(11)                    | NO   |     | 123              |                |
| email    | varchar(50)                | NO   |     | 382771946@qq.com |                |
| age      | tinyint(3) unsigned        | YES  |     | 18               |                |
| sex      | enum('男','女','保密') | YES  |     | 保密           |                |
| addr     | varchar(200)               | NO   |     | 北京           |                |
| salary   | float(6,2)                 | YES  |     | NULL             |                |
| regTime  | int(10) unsigned           | YES  |     | NULL             |                |
| face     | char(100)                  | NO   |     | default.jpg      |                |
| test6    | set('A','B','C')           | YES  |     | NULL             |                |
+----------+----------------------------+------+-----+------------------+----------------+
15 rows in set (0.00 sec)

– 删除test6字段

ALTER TABLE user10 DROP test6;

– 一次删除test2,test3,test4,test5

ALTER TABLE user10

DROP test2,

DROP test3,

DROP test4,

DROP test5;

mysql> DESC user10;
+----------+----------------------------+------+-----+------------------+----------------+
| Field    | Type                       | Null | Key | Default          | Extra          |
+----------+----------------------------+------+-----+------------------+----------------+
| id       | smallint(5) unsigned       | NO   | PRI | NULL             | auto_increment |
| username | varchar(20)                | NO   | UNI | NULL             |                |
| password | char(32)                   | NO   |     | NULL             |                |
| email    | varchar(50)                | NO   |     | 382771946@qq.com |                |
| age      | tinyint(3) unsigned        | YES  |     | 18               |                |
| sex      | enum('男','女','保密') | YES  |     | 保密           |                |
| addr     | varchar(200)               | NO   |     | 北京           |                |
| salary   | float(6,2)                 | YES  |     | NULL             |                |
| regTime  | int(10) unsigned           | YES  |     | NULL             |                |
| face     | char(100)                  | NO   |     | default.jpg      |                |
| test6    | set('A','B','C')           | YES  |     | NULL             |                |
+----------+----------------------------+------+-----+------------------+----------------+

－－修改字段

ALTER TABLE tbl_name MODIFY 字段名称 字段类型［完整性约束条件］［FIRST］［AFTER 字段名称］

将user10的email字段修改为VARCHAR（200）

ALTER TABLE user10 MODIFY email VARCHAR(200);

ALTER TABLE user10 MODIFY email VARCHAR(50) NOT NULL DEFAULT ‘382771946@qq.com’;

– 将card字段移动到test字段之后

ALTER TABLE user10 MODIFY card CHAR(18) AFTER test;

– 将test字段修改为CHAR(32) NOT NULL DEFAULT ‘123’ 移动到第一个位置

ALTER TABLE user10 MODIFY test CHAR(32) NOT NULL DEFAULT ‘123’ FIRST;

– 将test字段改为test1

ALTER TABLE user10 CHANGE test test1 CHAR(32) NOT NULL DEFAULT ‘123’;

ALTER TABLE user10 CHANGE test1 test VARCHAR(200) NOT NULL AFTER username;

ALTER TABLE user10 CHANGE test test INT;

CREATE TABLE IF NOT EXISTS user11(

id TINYINT UNSIGNED KEY AUTO_INCREMENT ,

username VARCHAR(20) NOT NULL UNIQUE,

age TINYINT UNSIGNED

);

ALTER TABLE user11 ALTER age SET DEFAULT 18;

ALTER TABLE user11 ADD email VARCHAR(50) ;

– 删除默认值

ALTER TABLE user11 ALTER age DROP DEFAULT;

ALTER TABLE user11 ALTER email DROP DEFAULT;

– 添加主键

CREATE TABLE IF NOT EXISTS test12(

id INT

);

ALTER TABLE test12 ADD PRIMARY KEY(id);

CREATE TABLE IF NOT EXISTS test13(

id INT,

card CHAR(18),

username VARCHAR(20) NOT NULL

);

ALTER TABLE test13 ADD PRIMARY KEY(id,card);

– 删除test12表的主键

ALTER TABLE test12 DROP PRIMARY KEY;

ALTER TABLE test13 DROP PRIMARY KEY;

ALTER TABLE test12 ADD CONSTRAINT symbol PRIMARY KEY index_type(id);

CREATE TABLE IF NOT EXISTS test14(

id INT UNSIGNED KEY AUTO_INCREMENT

);

ALTER TABLE test14 MODIFY id INT UNSIGNED;

ALTER TABLE test14 DROP PRIMARY KEY ;