mysql学习笔记之表的基本操作

2024-07-24 13:12:16

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创建表

create table 表名

create table if not exists 表名

mysql> create database company;Query OK, 1 row affected (0.00 sec)mysql> use company;Database changedmysql> create table if not exists t_dept(  -> deptno int,  -> dname varchar(20),  -> loc varchar(40));Query OK, 0 rows affected (0.20 sec)mysql> show tables;+-------------------+| Tables_in_company |+-------------------+| t_dept      |+-------------------+1 row in set (0.00 sec)mysql>

显示当前库下的所有表

show tables;

mysql> show tables;+-------------------+| Tables_in_company |+-------------------+| t_dept      |+-------------------+1 row in set (0.00 sec)

查看表的结构

describe 表名

简写

desc 表名

mysql> describe t_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+3 rows in set (0.00 sec)mysql> desc t_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+3 rows in set (0.00 sec)

查看表的详细

show create table 表名

mysql> show create table t_dept;+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+| Table | Create Table                                                                            |+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+| t_dept | CREATE TABLE `t_dept` ( `deptno` int(11) DEFAULT NULL, `dname` varchar(20) DEFAULT NULL, `loc` varchar(40) DEFAULT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf8 |+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------+1 row in set (0.00 sec)show create table t_dept /Gmysql> show create table t_dept /G*************************** 1. row ***************************    Table: t_deptCreate Table: CREATE TABLE `t_dept` ( `deptno` int(11) DEFAULT NULL, `dname` varchar(20) DEFAULT NULL, `loc` varchar(40) DEFAULT NULL) ENGINE=InnoDB DEFAULT CHARSET=utf81 row in set (0.00 sec)

删除表

drop table 表名
drop table if exists 表名

mysql> drop table if exists t_dept;Query OK, 0 rows affected (0.12 sec)mysql> show tables;Empty set (0.00 sec)

修改表名

ALTER TABLE old_table_name RENAME [TO] new_table_name
old_table_name 原表名
new_table_name 新表名
将t_dept修改为tab_dept

mysql> alter table t_dept rename tab_dept;Query OK, 0 rows affected (0.09 sec)mysql> show tables;+-------------------+| Tables_in_company |+-------------------+| tab_dept     |+-------------------+1 row in set (0.00 sec)mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+3 rows in set (0.00 sec)

为表增加一个字段默认在最后
ALTER TABLE table_name ADD 属性名属性类型

为tab_dept增加一个字段descri varchar(20)

mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+3 rows in set (0.00 sec)mysql> alter table tab_dept add descri varchar(20);Query OK, 0 rows affected (0.33 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | varchar(20) | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+4 rows in set (0.00 sec)

在表的第一个位置增加一个字段

ALTER TABLE table_name ADD 属性名属性类型 first

mysql> alter table tab_dept add id int first;Query OK, 0 rows affected (0.38 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| id   | int(11)   | YES |   | NULL  |    || deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | varchar(20) | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+5 rows in set (0.00 sec)

在表的指定字段之后增加字段

ALTER TABLE table_name ADD 属性名属性类型 AFTER 属性名

mysql> alter table tab_dept add comm varchar(20) after dname;Query OK, 0 rows affected (0.31 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| id   | int(11)   | YES |   | NULL  |    || deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || comm  | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | varchar(20) | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+6 rows in set (0.00 sec)

删除字段

ALTER TABLE table_name DROP 属性名

mysql> alter table tab_dept drop comm;Query OK, 0 rows affected (0.32 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| id   | int(11)   | YES |   | NULL  |    || deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | varchar(20) | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+5 rows in set (0.00 sec)

字段修改-修改字段数据类型
ALTER TABLE table_name MODIFY 属性名数据类型

mysql> alter table tab_dept modify descri int;Query OK, 0 rows affected (0.45 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| id   | int(11)   | YES |   | NULL  |    || deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | int(11)   | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+5 rows in set (0.00 sec)

字段修改-修改字段名称

ALTER TABLE table_name CHANGE 旧属性名新属性名旧数据类型

mysql> alter table tab_dept change id deptid int;Query OK, 0 rows affected (0.07 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| deptid | int(11)   | YES |   | NULL  |    || deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | int(11)   | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+5 rows in set (0.00 sec)

字段修改-同时修改字段名称与数据类型

ALTER TABLE table_name CHANGE 旧属性名新属性名新数据类型

mysql> alter table tab_dept change deptid id varchar(32);Query OK, 0 rows affected (0.49 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| id   | varchar(32) | YES |   | NULL  |    || deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | int(11)   | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+5 rows in set (0.00 sec)

修改顺序

ALTER TABLE table_name MODIFY 属性名1 数据类型 FIRST|AFTER 属性名2

2个属性必须存在
将deptno调到第一个位置

mysql> alter table tab_dept modify deptno int first;Query OK, 0 rows affected (0.33 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| deptno | int(11)   | YES |   | NULL  |    || id   | varchar(32) | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | int(11)   | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+5 rows in set (0.00 sec)

将ID放在最后

mysql> alter table tab_dept modify deptno int after descri;Query OK, 0 rows affected (0.29 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| id   | varchar(32) | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | int(11)   | YES |   | NULL  |    || deptno | int(11)   | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+5 rows in set (0.00 sec)mysql> alter table tab_dept modify deptno int first;Query OK, 0 rows affected (0.34 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> alter table tab_dept modify id int after descri;Query OK, 0 rows affected (0.47 sec)Records: 0 Duplicates: 0 Warnings: 0mysql> desc tab_dept;+--------+-------------+------+-----+---------+-------+| Field | Type    | Null | Key | Default | Extra |+--------+-------------+------+-----+---------+-------+| deptno | int(11)   | YES |   | NULL  |    || dname | varchar(20) | YES |   | NULL  |    || loc  | varchar(40) | YES |   | NULL  |    || descri | int(11)   | YES |   | NULL  |    || id   | int(11)   | YES |   | NULL  |    |+--------+-------------+------+-----+---------+-------+5 rows in set (0.00 sec)

注：相关教程知识阅读请移步到MYSQL教程频道。

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