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MySQL数据表操作实战
2022-08-03 13:01:00 【bojiSAMA】
操作流程
创建数据库Market，在Market中创建数据表customers，customers 表结构如下图所示，按要求进行操作
操作1：
mysql> create database Market; #该行为执行操作
Query OK, 1 row affected (0.00 sec)
mysql> create table customers( c_num int(11)primary key not null UNIQUE AUTO_INCREMENT,c_name varchar(50),c_contact varchar(50),c_birth datetime not null);
Query OK, 0 rows affected (0.01 sec)
- 创建数据库Market。
在操作1已经完成 - 创建数据表customers，在c_num字段上添加主键约束和自增约
束，在c_birth字段上添加非空约束。在操作1已经完成 - 将c_contact字段插入到c_birth字段后面。
mysql> alter table customers modify c_contact varchar(50) after c_birth;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc customers;
+-----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+----------------+
| c_num | int(11) | NO | PRI | NULL | auto_increment |
| c_name | varchar(50) | YES | | NULL | |
| c_birth | datetime | NO | | NULL | |
| c_contact | varchar(50) | YES | | NULL | |
+-----------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
- 将c_name字段数据类型改为VARCHAR(70)。
mysql> alter table customers MODIFY c_name varchar(70);
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc customers;
+-----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+----------------+
| c_num | int(11) | NO | PRI | NULL | auto_increment |
| c_name | varchar(70) | YES | | NULL | |
| c_birth | datetime | NO | | NULL | |
| c_contact | varchar(50) | YES | | NULL | |
+-----------+-------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)
- 将c_contact字段名改为c_phone,数据类型保持不变
mysql> alter table customers CHANGE c_contact c_phone varchar(50);
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc customers;
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| c_num | int(11) | NO | PRI | NULL | auto_increment |
| c_name | varchar(70) | YES | | NULL | |
| c_birth | datetime | NO | | NULL | |
| c_phone | varchar(50) | YES | | NULL | |
+---------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
- 增加c_gender字段，数据类型为CHAR(1)。
mysql> alter table customers add c_gender char(1);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc customers;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| c_num | int(11) | NO | PRI | NULL | auto_increment |
| c_name | varchar(70) | YES | | NULL | |
| c_birth | datetime | NO | | NULL | |
| c_phone | varchar(50) | YES | | NULL | |
| c_gender | char(1) | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
5 rows in set (0.01 sec)
- 将表名修改为customers_info。
mysql> alter table customers RENAME customers_info;
Query OK, 0 rows affected (0.00 sec)
mysql> show tables;
+------------------+
| Tables_in_Market |
+------------------+
| customers_info |
+------------------+
1 row in set (0.00 sec)
- 创建数据类型为varchar(50)的c_city字段 后 删除该字段。
mysql> alter table customers_info add c_city varchar(50); #添加字段操作
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc customers_info;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| c_num | int(11) | NO | PRI | NULL | auto_increment |
| c_name | varchar(70) | YES | | NULL | |
| c_birth | datetime | NO | | NULL | |
| c_phone | varchar(50) | YES | | NULL | |
| c_gender | char(1) | YES | | NULL | |
| c_city | varchar(50) | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)
mysql> alter table customers_info drop c_city; #删除字段操作
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc customers_info
-> ;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| c_num | int(11) | NO | PRI | NULL | auto_increment |
| c_name | varchar(70) | YES | | NULL | |
| c_birth | datetime | NO | | NULL | |
| c_phone | varchar(50) | YES | | NULL | |
| c_gender | char(1) | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
- 修改数据表的存储引擎为MyISAM。
mysql> alter table customers_info engine MyISAM;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table customers_info\G;# \G为规范化显示
*************************** 1. row ***************************
Table: customers_info
Create Table: CREATE TABLE `customers_info` (
`c_num` int(11) NOT NULL AUTO_INCREMENT,
`c_name` varchar(70) DEFAULT NULL,
`c_birth` datetime NOT NULL,
`c_phone` varchar(50) DEFAULT NULL,
`c_gender` char(1) DEFAULT NULL,
PRIMARY KEY (`c_num`),
UNIQUE KEY `c_num` (`c_num`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 #可以看到engine已经变成了MyISAM，查看数据库支持的所有引擎可通过show engines\G；来查
1 row in set (0.00 sec)
在Market中创建数据表orders，orders表结构如下表所示，按要求进行操作。
⑴创建数据表orders，在c_num字段上添加主键约束和自增约束， 在c_id字段上添加外键约束，关联customers表中的主键c_num。
#必须先把表引擎都设为Innodb
mysql> alter table customers_info engine=innodb
-> ;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table customers_info\G #规范化结束输出显示
*************************** 1. row ***************************
Table: customers_info
Create Table: CREATE TABLE `customers_info` (
`c_num` int(11) NOT NULL AUTO_INCREMENT,
`c_name` varchar(70) DEFAULT NULL,
`c_birth` datetime NOT NULL,
`c_phone` varchar(50) DEFAULT NULL,
`c_gender` char(1) DEFAULT NULL,
PRIMARY KEY (`c_num`),
UNIQUE KEY `c_num` (`c_num`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql> create table orders(c_num int(11) primary key not null unique AUTO_INCREMENT,o_date date,c_id int(11),CONSTRAINT xxxxxx FOREIGN KEY(c_id)REFERENCES customers_info(c_num))ENGINE=InnoDB DEFAULT CHARSET=laatin1;
Query OK, 0 rows affected (0.01 sec)
mysql> show create table orders\G
*************************** 1. row ***************************
Table: orders
Create Table: CREATE TABLE `orders` (
`c_num` int(11) NOT NULL AUTO_INCREMENT,
`o_date` date DEFAULT NULL,
`c_id` int(11) DEFAULT NULL,
PRIMARY KEY (`c_num`),
UNIQUE KEY `c_num` (`c_num`),
KEY `xxxxxx` (`c_id`),
CONSTRAINT `xxxxxx` FOREIGN KEY (`c_id`) REFERENCES `customers_info` (`c_num`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
# 如果两个表都是MyISAM 引擎的，即使设定外键也不会产生外键)
⑵删除orders表的外键约束，然后删除表customers_info。
mysql> drop table customers_info
-> ;
ERROR 1217 (23000): Cannot delete or update a parent row: a foreign key constraint fails
#当有外键关联本(父)表的时候，本(父)表无法被删除
mysql> alter table orders drop foreign key xxxxxx;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table orders\G
*************************** 1. row ***************************
Table: orders
Create Table: CREATE TABLE `orders` (
`c_num` int(11) NOT NULL AUTO_INCREMENT,
`o_date` date DEFAULT NULL,
`c_id` int(11) DEFAULT NULL,
PRIMARY KEY (`c_num`),
UNIQUE KEY `c_num` (`c_num`),
KEY `xxxxxx` (`c_id`) #可以看到外键约束被删除
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql> drop table customers_info;
Query OK, 0 rows affected (0.00 sec) #外键约束被删除后即可成功删除父表。
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