MySQL开发应该必须掌握的sql语句

下面一起来了解下MySQL开发应该必须掌握的sql语句，相信大家看完肯定会受益匪浅，文字在精不在多，希望MySQL开发应该必须掌握的sql语句这篇短内容是你想要的。

创建数据库

create database db1;

删除数据库

drop database db1;

创建数据表

create table tb1用户表(                    id int not null auto_increment primary key,                    name char(10),                    department_id int,                    p_id int,                )engine=innodb default charset=utf8;

主键（primary key）一个表只能有一个主键，主键可以由一列或者多列组成

外键的创建

CREATE TABLE t5 (                      nid int(11) NOT NULL AUTO_INCREMENT,                      pid int(11) not NULL,                      num int(11),                      primary key(nid,pid) --这里就是把两列设置成了主键                    ) ENGINE=InnoDB DEFAULT CHARSET=utf8;                    create table t6(                        id int auto_increment primary key,                        name char(10),                        id1 int,                        id2 int,                        CONSTRAINT fk_t5_t6 foreign key (id1,id2) REFERENCES t1(nid,pid) --这里是设置外键                    )engine=innodb default charset=utf8;

数据行的操作

数据的插入

insert into tb1(name,age) values('ax',8);insert into tb12(name,age) select name,age from tb11;

表中的数据的删除

delete from t1;truncate table t1;drop table t1delete from tb1 where id > 10delete from tb12 where id >=2 or name='alex'

数据的更新

update tb1 set name='root' where id > 10

数据的查询

select * from tb;select id,name from tb;

表结构的查看

show create table t1;desc t1;

其他

  select * from tb12 where id != 1    select * from tb12 where id in (1,5,12);    select * from tb12 where id not in (1,5,12);    select * from tb12 where id in (select id from tb11)    select * from tb12 where id between 5 and 12;

通配符

select * from tb12 where name like "a%"select * from tb12 where name like "a_"

分页

select * from tb12 limit 10;                    select * from tb12 limit 0,10;select * from tb12 limit 10,10;select * from tb12 limit 20,10;                 select * from tb12 limit 10 offset 20;# page = input('请输入要查看的页码')# page = int(page)# (page-1) * 10# select * from tb12 limit 0,10; 1 # select * from tb12 limit 10,10;2

排序

select * from tb12 order by id desc; 大到小select * from tb12 order by id asc;  小到大select * from tb12 order by age desc,id desc;取后10条数据select * from tb12 order by id desc limit 10;

分组

select count(id),max(id),part_id from userinfo5 group by part_id;聚合函数有下面几个：                                      count                    max                    min                    sum                    avg**** 如果对于聚合函数结果进行二次筛选时？必须使用having ****select count(id),part_id from userinfo5 group by part_id having count(id) > 1;select count(id),part_id from userinfo5 where id > 0 group by part_id having count(id) > 1;

自增值设置

表自增值的设置

alter table t1 auto_increment=20;-- 这个就表示从开始20开始算，用上面的show create table t1\G 就可以看到当前的值是多少。

基于会话级别

-- 查看当前的会话值show session variables like 'auto_incre%'-- 设置会话步长set session auto_increment_increment=2;-- 设置起始值set session auto_increment_offset=10;

基于全局设置

-- 查看全局的设置值show global variables like 'auto_inc%';-- 设置全局步长值set global auto_increment_increment=3;-- 设置起始值set global auto_increment_offset=11;

sql server 是在创建表的时候就可以自己设置，灵活度很高
REATE TABLE t5 (
nid int(11) NOT NULL AUTO_INCREMENT,
pid int(11) NOT NULL,
num int(11) DEFAULT NULL,
PRIMARY KEY (nid,pid)
) ENGINE=InnoDB AUTO_INCREMENT=4, 步长=2 DEFAULT CHARSET=utf8

          CREATE TABLE `t6` (

nid int(11) NOT NULL AUTO_INCREMENT,
pid int(11) NOT NULL,
num int(11) DEFAULT NULL,
PRIMARY KEY (nid,pid)
) ENGINE=InnoDB AUTO_INCREMENT=4, 步长=20 DEFAULT CHARSET=utf8

唯一索引

create table t1(    id int,    num int,    xx int,    unique qu1 (num ,xx) -- 意思就是这两列在一行上面数据不能相同，例如都是1,1,就不行);

唯一索引：约束不能重复（可以为空）
主键索引：约束不能重复（不可以为空）
他们的特点都是加速查询

外键一对一

create table userinfo1(                    id int auto_increment primary key,                    name char(10),                    gender char(10),                    email varchar(64)                )engine=innodb default charset=utf8;                create table admin(                    id int not null auto_increment primary key,                    username varchar(64) not null,                    password VARCHAR(64) not null,                    user_id int not null,                    unique uq_u1 (user_id),                    CONSTRAINT fk_admin_u1 FOREIGN key (user_id) REFERENCES userinfo1(id)                )engine=innodb default charset=utf8;

外键多对多

示例1：                用户表                相亲表            示例2：                用户表                主机表                用户主机关系表            ===》多对多                create table userinfo2(                    id int auto_increment primary key,                    name char(10),                    gender char(10),                    email varchar(64)                )engine=innodb default charset=utf8;                create table host(                    id int auto_increment primary key,                    hostname char(64)                )engine=innodb default charset=utf8;                create table user2host(                    id int auto_increment primary key,                    userid int not null,                    hostid int not null,                    unique uq_user_host (userid,hostid),                    CONSTRAINT fk_u2h_user FOREIGN key (userid) REFERENCES userinfo2(id),                    CONSTRAINT fk_u2h_host FOREIGN key (hostid) REFERENCES host(id)                )engine=innodb default charset=utf8;

连表操作

select * from userinfo5,department5                    select * from userinfo5,department5 where userinfo5.part_id = department5.id                    select * from userinfo5 left join department5 on userinfo5.part_id = department5.id                    select * from department5 left join userinfo5 on userinfo5.part_id = department5.id                    # userinfo5左边全部显示                    # select * from userinfo5 right join department5 on userinfo5.part_id = department5.id                    # department5右边全部显示                    select * from userinfo5 innder join department5 on userinfo5.part_id = department5.id                    将出现null时一行隐藏select * from                         department5 left join userinfo5 on userinfo5.part_id = department5.idleft join userinfo6 on userinfo5.part_id = department5.idselect                         score.sid,                        student.sid from                     scoreleft join student on score.student_id = student.sidleft join course on score.course_id = course.cidleft join class on student.class_id = class.cidleft join teacher on course.teacher_id=teacher.ti          
select count(id) from userinfo5;

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