MySQL增删改查的常用操作指令总结

总结：
1、数据库操作：
创建库：
    create database db_name;

查询库：
    show databases;     //显示所有的数据库
    show create databases db_name; //显示特定的数据库

删除库：
    drop database db_name;

修改库：
    alter database db_name [modify command];
    alter database db_name character set gbk;

2、表操作：
创建表：
    use db_name;
    create table tbl_name (column_structure) [tbl_option];
如：
    create table tbl_name(
    variable_name1 varchar(10)
    variable_name2 int
    );
或 create table db_name.tbl_name(
    variable_name1 varchar(10)
    variable_name2 int
    );

查询表：
查看有哪些表：   
    show tables;
或show tables like ‘pattern_%‘;
查看表的创建信息：
    show create table tbl_name; 
或show create table tbl_name \G
查看表的结构：
    describe tbl_name;
或desc tbl_name;]

删除表：
    drop table [if exists] tbl_name;

修改表：
修改表名：
单个：rename table old_tbl_name to new_tbl_name;
多个：rename table old_tbl_name1 to new_tbl_name1, old_tbl_name2 to new_tbl_name2;
跨数据库：rename table old_tbl_name to db_name.new_tbl_name;
修改列定义：
增加新列定义：add
    alter table tbl_name add new_column_name data_type;  
如alter table exam_student add height int;
修改列的定义(新的属性或者数据类型)：modify
    alter table tbl_name modify column_name new_data_type;
删除一个列：drop
    alter table tbl_name drop column_name;
重命名一个列：change
    alter table tbl_name change old_column_name new_column_name new_data_type;
修改表选项：
    alter table tbl_name new_tbl_option;
    alter table tbl_name character set utf8;

3、数据操作：
创建数据：
    insert into tbl_name (fields_list) values (values_list);
如：insert into exam_student (stu_name, stu_no) values (‘xiaoming‘, ‘php030_01‘);
若插入所有字段值：
insert into exam_student values (‘xiaoming‘, ‘php030_01‘, 98);

查询数据：
查看字段信息：
    select * from tbl_name;
参看具体字段列表信息：    
select fields_list from tbl_name where condition;
如：默认状态下select stu_name, stu_no from exam_student;
或：select stu_name, stu_no from exam_student where 1;
有条件查询：
select * from tbl_name where condition;
如select * from exam_student where fenshu >= 60;

删除数据：
    delete from tbl_name condition;
如delete from exam_student where fenshu <= 50;

修改数据：
    update tbl_name set field = new_value where condition;
如：update exam_student set fenshu =100 where fenshu >= 97;

4、主键：primary
如：法一：
create table teacher(
t_id int primary key [auto_increment],
t_name varchar(5),
class_name varchar(6),
t_days tinyint unsigned
);
法二：
create table teacher(
t_id int,
t_name varchar(5),
class_name varchar(6),
t_day tinyint unsigned,
primary key (t_id)
);
insert into teacher values (1, ‘王老师‘, ‘0225‘, 23);
自动增长：auto_increment
    alter table tbl_name auto_increment initial_value;

5、外键：foreign key
如：
主表：
create table itcast_class(
class_id int primary key auto_increment,
class_name varchar(10) not null default ‘itcast_php‘ comment ‘班级名称‘
) character set utf8;
从表：
create table itcast_student(
stu_id int primary key auto_increment,
stu_name varchar(10) not null default ‘‘,
class_id int,
foreign key (class_id) references itcast_class (class_id)
) character set utf8;
插入数据的顺序：先主表，后从表
insert into itcast_class values (null, ‘php0331‘);
insert into itcast_student values (null, ‘张三‘, 1);
删除操作：
alter table itcast_student drop foreign key itcast_student_ibfk_1;
alter table itcast_student add foreign key (class_id) references itcast_class (class_id) 
on delete set null;/*主表里删除某个字段，从表若对应外键则变成null*/
或者
on delete cascade;/*主表删除一个字段，从表对应的外键则会删除相应的值*/
又或者
on update restrict;/*不允许主表进行更新操作*/
delete from itcast_class where class_id = 1;