mysql之对表的操作

1. 表的基本概念

在数据库中,表是一种非常重要的数据库对象,是组成数据库的基本对象,由若干个字段组成,主要用来储存数据记录。

表中的数据库对象包含列,索引和触发器。

列:也称属性列，在具体创建表时必须指定列的名字和数据类型。

索引:是根据指定的数据库表列建立起来的顺序，提供了快速访问数据的途径且可监督表的数据,使其索引所指向的列中的数据不重复。

触发器:定义的事物命令的集合,当对一个表中的数据进行插入,更新或者删除时这组命令就会自动执行,可以用来确保数据的完整性和安全性。

2.创建表

CREATE TABLE t_dept(
deptno INT,
dbname VARCHAR(20),
loc VARCHAR(40)
);

3.查看表结构

3.1 DESCRIBE(DESC是简写)语句查看表定义

DESCRIBE t_dept;

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" 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3.2 SHOW CREATE TABLE语句查看表详细定义

SHOW CREATE TABLE  t_dept;

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" alt="" />

在显示详细定义信息时,可以使用";","\g"和"\G"符号来结束,为了让结果美观,便于查看，最好使用"\G"符号来结束,如下:

aaarticlea/png;base64,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" alt="" />

4. 删除表

DROP TABLE t_dept;

5. 修改表

5.1 修改表名

ALTER TABLE old_table_name RENAME [TO] NEW _table_name

5.2 增加字段

在表的最后一个位置增加字段:

ALTER TABLE table_name ADD 属性名 属性类型

在表的第一个位置增加字段:

ALTER TABLE table_name ADD 属性名 属性类型 FIRST

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

5.3 删除字段

ALTER TABLE table_name DROP 属性名

5.4 修改字段

修改字段的数据类型:

ALTER TABLE table_name MODIFY属性名 属性类型

修改字段的名字:

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

同时修改字段的名字和属性:

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

修改字段的顺序:

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

6. 操作表的约束

对于已经创建好的表,虽然字段的数据类型决定了所能储存的数据类型,但是表中所储存的数据是否合法并没有进行检查。如果想针对表中的数据做一些完整性检查操作,可以通过表中的约束来完成。

6.1 MySQL支持的完整性约束

所谓表的完整性是指数据的准确性和一致性,而完整性检查就是指检查数据的准确性和一致性。

完整性约束

完整性约束关键字	含义
NOT NULL	约束字段的值不能为空
DEFAULT	设置字段的默认值
UNIQUE KEY(UK)	约束字段的值是唯一
PRIMARY KEY(PK)	约束字段为表的主键,可以作为该表记录的唯一标识
AUTO_INCREMENT	约束字段的值为自动增加
FOREIGN KEY(FK)	约束字段为表的外键

MySQL数据库管理系统不支持check约束,即可以使用check约束但是却没有任何效果。

根据约束数据列限制,约束可以分为单列约束(每个约束只约束一列数据)和多列约束(每个约束可以约束多列数据)。

6.2 设置非空约束(NOT NULL,NK)

create table table_name(
属性名  属性类型 NOT NULL,

...
);

6.3 设置字段的默认值(DEFAULT)

create table table_name(
属性名  属性类型 DEFAULT 默认值,

...
);

6.4 设置唯一约束(UNIQUE,UK)

create table table_name(
属性名  属性类型 UNIQUE,

...
);

如果想给设置唯一约束的字段的约束取一个名字，可以执行SQL语句CONSTRAINT:

create table table_name(
dbname 属性类型,

...
CONSTRAINT uk_dbname UNIQUE(dbname)
);

6.5 设置主键约束(PRIMARY KEY,PK)

设置主键约束时,必须满足主键字段的值是唯一，非空的。

单字段主键：

create table table_name(
属性名  属性类型 PRIMARY KEY,

...
);

如果想给设置单一主键的字段的约束取一个名字，可以执行SQL语句CONSTRAINT:

create table table_name(
dbname 属性类型,

...
CONSTRAINT pk_dbname PRIMARY KEY(dbname)
);

多字段主键:

当主键由多个字段组合而成时,需要通过SQL语句CONSTRAINT 来实现:

create table table_name(
属性名1 数据类型,
属性名2 数据类型,

...
CONSTRAINT 约束名 PRIMARY KEY(属性名1，属性名2)
);

6.6 设置字段值自动增长(AUTO_INCREMENT)

AUTO_INCREMENT是MySQL唯一拓展的完整性约束,当为数据库表中插入新纪录时,字段上的值会自动生成唯一的ID。一个数据库表中只能有一个字段使用该约束,该字段的数据类型必须是整数类型。由于设置AUTO_INCREMENT约束后的字段会生成唯一的ID,所以该字段也经常会设置成PK主键。

create table table_name(
属性名  数据类型 AUTO_INCREMENT,

...
);

6.7 设置外键约束(FOREIGN KEY,FK)

前面的完整性约束都是在单表中进行设置,而外键约束则保证多个表(通常为两个表)之间的参照完整性,即构建于两个表的两个字段之间的参照关系。

create table table_name(
属性名 数据类型,
属性名 数据类型,

...
CONSTRAINT 外键约束名 FOREIGN KEY(属性名1) REFERENCES 表名 (属性名2)
);