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  • MySQL学习之SQL基础(一)DDL

    Sql基础

    DDL (data defination language)

    创建表

    CREATE TABLE emp(
    ename varchar(10),
    hiredate date,
    sal decimal(10,2),
    deptno int(2)
    );

    mysql> show create table emp;
    +-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
    
    | Table | Create Table                                                                                                                                                                                                                                    |
    
    +-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
    
    | emp  | CREATE TABLE `emp` (
    
      `ename` varchar(10) COLLATE utf8_unicode_ci DEFAULT NULL,
    
      `hiredate` date DEFAULT NULL,
    
      `sal` decimal(10,2) DEFAULT NULL,
    
      `deptno` int(2) DEFAULT NULL
    
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |
    
    +-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
    
    1 row in set (0.01 sec)
    
    

    修改表

    • 修改表类型
    ALTER TABLE emp  modify column ename varchar(20);
    
    ALTER TABLE emp  modify  ename varchar(25);
    
    
    • 增加表字段
    ALTER TABLE emp add column age int (3);
    
    
    • 删除表字段
    ALTER TABLE  emp drop column age;
    
    • 字段改名
    ALTER TABLE emp change age age1 int(5);
    
    • 修改顺序
    mysql> ALTER TABLE emp add column age int (4) AFTER ename;
    Query OK, 0 rows affected (0.06 sec)
    Records: 0  Duplicates: 0  Warnings: 0
    mysql> desc emp;
    +----------+---------------+------+-----+---------+-------+
    
    | Field    | Type          | Null | Key | Default | Extra |
    
    +----------+---------------+------+-----+---------+-------+
    
    | ename    | varchar(25)  | YES  |    | NULL    |      |
    
    | age      | int(4)        | YES  |    | NULL    |      |
    
    | hiredate | date          | YES  |    | NULL    |      |
    
    | sal      | decimal(10,2) | YES  |    | NULL    |      |
    
    | deptno  | int(2)        | YES  |    | NULL    |      |
    
    +----------+---------------+------+-----+---------+-------+
    
    
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  • 原文地址:https://www.cnblogs.com/JuncaiF/p/11153292.html
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