本文談談MySQL的開發必會的sql語句

創建數據庫

create database db1;

刪除數據庫

drop database db1;

創建數據表

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

主鍵（primary key）一個表只能有一個主鍵，主鍵可以由一列或者多列組成

外鍵的創建

CREATE TABLE t5 (
                      nid int(11) NOT NULL AUTO_INCREMENT,
                      pid int(11) not NULL,
                      num int(11),
                      primary key(nid,pid) --這里就是把兩列設置成了主鍵
                    ) 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) --這里是設置外鍵
                    )engine=innodb default charset=utf8;

數據行的操作

數據的插入

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

表中的數據的刪除

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

數據的更新

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

數據的查詢

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

表結構的查看

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_"

分頁

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('請輸入要查看的頁碼')
# 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條數據
select * from tb12 order by id desc limit 10;

分組

select count(id),max(id),part_id from userinfo5 group by part_id;
聚合函數有下面幾個：                  
                    count
                    max
                    min
                    sum
                    avg

**** 如果對于聚合函數結果進行二次篩選時？必須使用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;

自增值設置

表自增值的設置

alter table t1 auto_increment=20;
-- 這個就表示從開始20開始算，用上面的show create table t1G 就可以看到當前的值是多少。

基于會話級別

-- 查看當前的會話值
show session variables like 'auto_incre%'
-- 設置會話步長
set session auto_increment_increment=2;
-- 設置起始值
set session auto_increment_offset=10;

基于全局設置

-- 查看全局的設置值
show global variables like 'auto_inc%';
-- 設置全局步長值
set global auto_increment_increment=3;
-- 設置起始值
set global auto_increment_offset=11;

sql server 是在創建表的時候就可以自己設置，靈活度很高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, 步長=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, 步長=20 DEFAULT CHARSET=utf8

唯一索引

create table t1(
    id int,
    num int,
    xx int,
    unique qu1 (num ,xx) -- 意思就是這兩列在一行上面數據不能相同，例如都是1,1,就不行
);

唯一索引：約束不能重復（可以為空）主鍵索引：約束不能重復（不可以為空）他們的特點都是加速查詢

外鍵一對一

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;

外鍵多對多

示例1：
                用戶表
                相親表

            示例2：
                用戶表
                主機表
                用戶主機關系表
            ===》多對多

                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;

連表操作

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左邊全部顯示

                    # select * from userinfo5 right join department5 on userinfo5.part_id = department5.id
                    # department5右邊全部顯示

                    select * from userinfo5 innder join department5 on userinfo5.part_id = department5.id
                    將出現null時一行隱藏

select * from 
                        department5 
left join userinfo5 on userinfo5.part_id = department5.id
left join userinfo6 on userinfo5.part_id = department5.id

select 
                        score.sid,
                        student.sid 
from 
                    score

left join student on score.student_id = student.sid

left join course on score.course_id = course.cid

left join class on student.class_id = class.cid

left join teacher on course.teacher_id=teacher.ti           

select count(id) from userinfo5;