环境：

 

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 命令：

(1)create database Market;

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(2)

create table customers(
c_num int(11) primary key auto_increment,
c_name varchar(50),
c_contact varchar(50),
c_city varchar(50),
c_birth datetime not null
);

 

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(3)

alter table customers modify column c_contact varchar(50) after c_birth;

 

 

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(4)

alter table customers modify column c_name varchar(70);

 

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(5)

alter table customers change c_contact c_phone varchar(50);

 

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(6)

alter table customers add c_gender char(1);

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(7) 

alter table customers rename to customers_info;

 

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(8)

alter table customers_info drop column c_city;

 

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(9)

alter table customers_info engine=MyISAM;

alter table customers_info engine=InnoDB;

 

=========================================================================

(1)

create table orders(
o_num int(11) primary key auto_increment,
o_date date,
c_id int(11),
foreign key (c_id) references customers_info (c_num)
);

 

 补充：InnoDB支持外键，MyISAM不支持外键

没有指定外键约束的名称，就会自动生成一个名称，这个名称不是列名字。

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(2) 

删除表的约束

#查看创建表的过程
show create table orders;

#删除外键约束
alter table orders drop foreign key orders_ibfk_1;

 

删除表

drop table customers_info;