mysql -uroot -p密码
show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| school |
| springboot |
| springdb |
| sys |
+--------------------+
create database ssm;
use ssm;
show tables;
+---------------+
| Tables_in_ssm |
+---------------+
| dept |
| emp |
| salgrade |
+---------------+
# (文件路径)
source G:\BaiduNetdiskDownload\Msq笔记\bjpowernode.sql
desc dept;
+--------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------+------+-----+---------+-------+
| DEPTNO | int(2) | NO | PRI | NULL | | 部门编号
| DNAME | varchar(14) | YES | | NULL | | 部门名称
| LOC | varchar(13) | YES | | NULL | | 部门位置
+--------+-------------+------+-----+---------+-------+
desc emp;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| EMPNO | int(4) | NO | PRI | NULL | | 员工编号
| ENAME | varchar(10) | YES | | NULL | | 员工姓名
| JOB | varchar(9) | YES | | NULL | | 工作岗位
| MGR | int(4) | YES | | NULL | | 上级领导编号
| HIREDATE | date | YES | | NULL | | 入职日期
| SAL | double(7,2) | YES | | NULL | | 月薪
| COMM | double(7,2) | YES | | NULL | | 补助
| DEPTNO | int(2) | YES | | NULL | | 部门编号
+----------+-------------+------+-----+---------+-------+
desc salgrade;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| GRADE | int(11) | YES | | NULL | | 等级
| LOSAL | int(11) | YES | | NULL | | 最低薪资
| HISAL | int(11) | YES | | NULL | | 最高薪资
+-------+---------+------+-----+---------+-------+
mysql> select * from dept;
+--------+------------+----------+
| DEPTNO | DNAME | LOC |
+--------+------------+----------+
| 10 | ACCOUNTING | NEW YORK |
| 20 | RESEARCH | DALLAS |
| 30 | SALES | CHICAGO |
| 40 | OPERATIONS | BOSTON |
+--------+------------+----------+
mysql> select * from emp;
+-------+--------+-----------+------+------------+---------+---------+--------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
+-------+--------+-----------+------+------------+---------+---------+--------+
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 |
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 |
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 |
| 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 |
+-------+--------+-----------+------+------------+---------+---------+--------+
mysql> select * from salgrade;
+-------+-------+-------+
| GRADE | LOSAL | HISAL |
+-------+-------+-------+
| 1 | 700 | 1200 |
| 2 | 1201 | 1400 |
| 3 | 1401 | 2000 |
| 4 | 2001 | 3000 |
| 5 | 3001 | 9999 |
+-------+-------+-------+
mysql --version
mysql -V
mysql Ver 8.0.17 for Win64 on x86_64 (MySQL Community Server - GPL)
select databases();
\c
ctrl + c
quit
show create table emp;
--------------------+
| emp | CREATE TABLE `emp` (
`EMPNO` int(4) NOT NULL,
`ENAME` varchar(10) DEFAULT NULL,
`JOB` varchar(9) DEFAULT NULL,
`MGR` int(4) DEFAULT NULL,
`HIREDATE` date DEFAULT NULL,
`SAL` double(7,2) DEFAULT NULL,
`COMM` double(7,2) DEFAULT NULL,
`DEPTNO` int(2) DEFAULT NULL,
PRIMARY KEY (`EMPNO`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |
show tables from springboot;
# 在Windows的dos命令窗口中执行
mysqldump ssm>D:\ssm.sql -uroot -p333
# 导入
create database ssm;
use ssm;
source D:\ssm.sql
char
: 不可变长度,当某个字段中的数据长度不发生改变的时候使用varchar
:可变长度,当某个字段中的数据长度不确定时使用BLOB
:二进制大对象(存储图片、视频等流媒体信息) Binary Large OBject (对应java中的Object)CLOB
:字符大对象(存储较大文本,比如,可以存储4G的字符串。) Character Large OBject(对应java中的Object)drop table if exists t_student;
insert into t_student(name,no) values ('zhangsan',2);
insert into t_student VALUES (1,'jack',0,'2000-01-01');
mysql> insert into t_student(name,no) values ('zhangsan',5),('zhangsan3',4);
mysql> select * from t_student;
+----+-----------+------+------------+
| no | name | sex | birth |
+----+-----------+------+------------+
| 1 | jack | 0 | 2000-01-01 |
| 2 | zhangsan | NULL | NULL |
| 3 | zhangsan2 | 0 | NULL |
| 4 | zhangsan3 | 0 | NULL |
| 5 | zhangsan | 0 | NULL |
+----+-----------+------+------------+
语法格式:
create table 表名 as select 语句;
没有条件整张表字段全部插入
mysql> create table t_student1 as select ename,deptno from emp;
Query OK, 14 rows affected (0.04 sec)
Records: 14 Duplicates: 0 Warnings: 0
mysql> select * from t_student1;
+--------+--------+
| ename | deptno |
+--------+--------+
| SMITH | 20 |
| ALLEN | 30 |
| WARD | 30 |
| JONES | 20 |
| MARTIN | 30 |
| BLAKE | 30 |
| CLARK | 10 |
| SCOTT | 20 |
| KING | 10 |
| TURNER | 30 |
| ADAMS | 20 |
| JAMES | 30 |
| FORD | 20 |
| MILLER | 10 |
+--------+--------+
mysql> insert into t_student1 select ename,deptno from emp;
Query OK, 14 rows affected (0.01 sec)
Records: 14 Duplicates: 0 Warnings: 0
mysql> select * from t_student1;
+--------+--------+
| ename | deptno |
+--------+--------+
| SMITH | 20 |
| ALLEN | 30 |
| WARD | 30 |
| JONES | 20 |
| MARTIN | 30 |
| BLAKE | 30 |
| CLARK | 10 |
| SCOTT | 20 |
| KING | 10 |
| TURNER | 30 |
| ADAMS | 20 |
| JAMES | 30 |
| FORD | 20 |
| MILLER | 10 |
| SMITH | 20 |
| ALLEN | 30 |
| WARD | 30 |
| JONES | 20 |
| MARTIN | 30 |
| BLAKE | 30 |
| CLARK | 10 |
| SCOTT | 20 |
| KING | 10 |
| TURNER | 30 |
| ADAMS | 20 |
| JAMES | 30 |
| FORD | 20 |
| MILLER | 10 |
+--------+--------+
28 rows in set (0.00 sec)
语法格式:
update 表名 set 字段名1=值1,字段名2=值2 ... where 条件
没有条件整张表全部更新
mysql> update t_student set sex = '1',name = 'ssm' where no = 1;
语法格式:
delete from 表名 where 条件;
没有条件全部删除。
mysql> delete from t_student where no = 5;
Query OK, 1 row affected (0.01 sec)
delete from t_student;
truncate table t_student1;
select 5
..
from 1
..
where 2
..
group by 3 分组函数在分组之后才能使用
..
having 4
..
order by 6
..
limit
.. 7
mysql> select empno,ename,sal*12 as yearsal from emp;
+-------+--------+----------+
| empno | ename | yearsal |
+-------+--------+----------+
| 7369 | SMITH | 9600.00 |
| 7499 | ALLEN | 19200.00 |
| 7521 | WARD | 15000.00 |
| 7566 | JONES | 35700.00 |
| 7654 | MARTIN | 15000.00 |
| 7698 | BLAKE | 34200.00 |
| 7782 | CLARK | 29400.00 |
| 7788 | SCOTT | 36000.00 |
| 7839 | KING | 60000.00 |
| 7844 | TURNER | 18000.00 |
| 7876 | ADAMS | 13200.00 |
| 7900 | JAMES | 11400.00 |
| 7902 | FORD | 36000.00 |
| 7934 | MILLER | 15600.00 |
+-------+--------+----------+
运算符 | 说明 |
---|---|
= | 等于 |
<>或!= | 不等于 |
< | 小于 |
<= | 小于等于 |
> | 大于 |
>= | 大于等于 |
between … and …. | 两个值之间,等同于 >= and <= 字符方面:左闭右开 |
is null | 为null(is not null 不为空) |
and | 并且 |
or | 或者 |
in | 包含,相当于多个or(not in不在这个范围中) |
not | not可以取非,主要用在is 或in中 |
like | like称为模糊查询,支持%或下划线匹配 %匹配任意个字符 下划线,一个下划线只匹配一个字符 |
mysql> select ename,sal from emp where sal between 1100 and 3100;
+--------+---------+
| ename | sal |
+--------+---------+
| ALLEN | 1600.00 |
| WARD | 1250.00 |
| JONES | 2975.00 |
| MARTIN | 1250.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| SCOTT | 3000.00 |
| TURNER | 1500.00 |
| ADAMS | 1100.00 |
| FORD | 3000.00 |
| MILLER | 1300.00 |
+--------+---------+
select ename,sal,comm from emp where comm is null or comm = 0.0;
+--------+---------+------+
| ename | sal | comm |
+--------+---------+------+
| SMITH | 800.00 | NULL |
| JONES | 2975.00 | NULL |
| BLAKE | 2850.00 | NULL |
| CLARK | 2450.00 | NULL |
| SCOTT | 3000.00 | NULL |
| KING | 5000.00 | NULL |
| TURNER | 1500.00 | 0.00 |
| ADAMS | 1100.00 | NULL |
| JAMES | 950.00 | NULL |
| FORD | 3000.00 | NULL |
| MILLER | 1300.00 | NULL |
+--------+---------+------+
mysql> select ename,sal,deptno from emp where sal>1000 and (deptno = 20 or deptno = 30);
+--------+---------+--------+
| ename | sal | deptno |
+--------+---------+--------+
| ALLEN | 1600.00 | 30 |
| WARD | 1250.00 | 30 |
| JONES | 2975.00 | 20 |
| MARTIN | 1250.00 | 30 |
| BLAKE | 2850.00 | 30 |
| SCOTT | 3000.00 | 20 |
| TURNER | 1500.00 | 30 |
| ADAMS | 1100.00 | 20 |
| FORD | 3000.00 | 20 |
+--------+---------+--------+
select ename,job,sal from emp where sal in(800,5000);
+-------+-----------+---------+
| ename | job | sal |
+-------+-----------+---------+
| SMITH | CLERK | 800.00 |
| KING | PRESIDENT | 5000.00 |
+-------+-----------+---------+
%
代表多个字符_
代表单个字符mysql> select * from emp where ename like 'M%';
+-------+--------+----------+------+------------+---------+---------+--------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
+-------+--------+----------+------+------------+---------+---------+--------+
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 |
+-------+--------+----------+------+------------+---------+---------+--------+
mysql> select * from emp where ename like '%N';
mysql> select * from emp where ename like '%O%';
mysql> select * from emp where ename like '__a%';
mysql> select * from emp where ename like '%\_%';
mysql> select * from emp order by job desc,sal desc;
+-------+--------+-----------+------+------------+---------+---------+--------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
+-------+--------+-----------+------+------------+---------+---------+--------+
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 |
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 |
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 |
| 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 |
+-------+--------+-----------+------+------------+---------+---------+--------+
mysql> select * from emp order by sal asc;
+-------+--------+-----------+------+------------+---------+---------+--------+
| EMPNO | ENAME | JOB | MGR | HIREDATE | SAL | COMM | DEPTNO |
+-------+--------+-----------+------+------------+---------+---------+--------+
| 7369 | SMITH | CLERK | 7902 | 1980-12-17 | 800.00 | NULL | 20 |
| 7900 | JAMES | CLERK | 7698 | 1981-12-03 | 950.00 | NULL | 30 |
| 7876 | ADAMS | CLERK | 7788 | 1987-05-23 | 1100.00 | NULL | 20 |
| 7521 | WARD | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 | 30 |
| 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 | 30 |
| 7934 | MILLER | CLERK | 7782 | 1982-01-23 | 1300.00 | NULL | 10 |
| 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 | 0.00 | 30 |
| 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 | 30 |
| 7782 | CLARK | MANAGER | 7839 | 1981-06-09 | 2450.00 | NULL | 10 |
| 7698 | BLAKE | MANAGER | 7839 | 1981-05-01 | 2850.00 | NULL | 30 |
| 7566 | JONES | MANAGER | 7839 | 1981-04-02 | 2975.00 | NULL | 20 |
| 7788 | SCOTT | ANALYST | 7566 | 1987-04-19 | 3000.00 | NULL | 20 |
| 7902 | FORD | ANALYST | 7566 | 1981-12-03 | 3000.00 | NULL | 20 |
| 7839 | KING | PRESIDENT | NULL | 1981-11-17 | 5000.00 | NULL | 10 |
+-------+--------+-----------+------+------------+---------+---------+--------+
函数 | 解释 |
---|---|
count | 取得记录数 |
sum | 求和 |
avg | 取平均 |
max | 取最大的数 |
min | 取最小的数 |
采用count(字段名称),不会取得为null的记录
select count(*) from emp;
select count(comm) from emp;
distinct
:去重 只能出现在所有字段的最前面select count(distinct job ) from emp;
+---------------------+
| count(distinct job) |
+---------------------+
| 5 |
+---------------------+
mysql> select sum(sal+ifnull(comm,0)) from emp;
+-------------------------+
| sum(sal+ifnull(comm,0)) |
+-------------------------+
| 31225.00 |
+-------------------------+
mysql> select avg(sal) from emp;
+-------------+
| avg(sal) |
+-------------+
| 2073.214286 |
+-------------+
mysql> select max(sal) from emp;
+----------+
| max(sal) |
+----------+
| 5000.00 |
+----------+
mysql> select max(str_to_date (hiredate, '%Y-%m-%d')) from emp;
+-----------------------------------------+
| max(str_to_date (hiredate, '%Y-%m-%d')) |
+-----------------------------------------+
| 1987-05-23 |
+-----------------------------------------+
select min(str_to_date(hiredate, '%Y-%m-%d')) from emp;
+----------------------------------------+
| min(str_to_date(hiredate, '%Y-%m-%d')) |
+----------------------------------------+
| 1980-12-17 |
+----------------------------------------+
select count(*),sum(sal),avg(sal),max(sal),min(sal) from emp;
+----------+----------+-------------+----------+----------+
| count(*) | sum(sal) | avg(sal) | max(sal) | min(sal) |
+----------+----------+-------------+----------+----------+
| 14 | 29025.00 | 2073.214286 | 5000.00 | 800.00 |
+----------+----------+-------------+----------+----------+
group by
:按照某个字段或者某些字段进行分组having
: 对分组之后的数据进行再次过滤where
后面不能使用分组函数,遇到这种情况就使用having
mysql>select deptno,job,max(sal) from emp group by deptno,job order by deptno;
+--------+-----------+----------+
| deptno | job | max(sal) |
+--------+-----------+----------+
| 10 | CLERK | 1300.00 |
| 10 | MANAGER | 2450.00 |
| 10 | PRESIDENT | 5000.00 |
| 20 | ANALYST | 3000.00 |
| 20 | CLERK | 1100.00 |
| 20 | MANAGER | 2975.00 |
| 30 | CLERK | 950.00 |
| 30 | MANAGER | 2850.00 |
| 30 | SALESMAN | 1600.00 |
+--------+-----------+----------+
order by
,order by
必须放到group by
后面mysql> select ename,sum(sal),job from emp group by job order by sum(sal) desc;
+-------+----------+-----------+
| ename | sum(sal) | job |
+-------+----------+-----------+
| JONES | 8275.00 | MANAGER |
| SCOTT | 6000.00 | ANALYST |
| ALLEN | 5600.00 | SALESMAN |
| KING | 5000.00 | PRESIDENT |
| SMITH | 4150.00 | CLERK |
+-------+----------+-----------+
mysql> select ename,sal from emp where sal > (select avg(sal) from emp);
+-------+---------+
| ename | sal |
+-------+---------+
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| SCOTT | 3000.00 |
| KING | 5000.00 |
| FORD | 3000.00 |
mysql> select deptno,avg(sal) from emp group by deptno having avg(sal)>2000;
+--------+-------------+
| deptno | avg(sal) |
+--------+-------------+
| 20 | 2175.000000 |
| 10 | 2916.666667 |
+--------+-------------+
...
A
join
B
on
连接条件
where
...
mysql> select e.ename,d.dname from emp e join dept d on e.deptno= d.deptno;
+--------+------------+
| ename | dname |
+--------+------------+
| SMITH | RESEARCH |
| ALLEN | SALES |
| WARD | SALES |
| JONES | RESEARCH |
| MARTIN | SALES |
| BLAKE | SALES |
| CLARK | ACCOUNTING |
| SCOTT | RESEARCH |
| KING | ACCOUNTING |
| TURNER | SALES |
| ADAMS | RESEARCH |
| JAMES | SALES |
| FORD | RESEARCH |
| MILLER | ACCOUNTING |
+--------+------------+
mysql> select e.ename,e.sal,s.grade from emp e join salgrade s on e.sal between s.losal and s.hisal;
+--------+---------+-------+
| ename | sal | grade |
+--------+---------+-------+
| SMITH | 800.00 | 1 |
| ALLEN | 1600.00 | 3 |
| WARD | 1250.00 | 2 |
| JONES | 2975.00 | 4 |
| MARTIN | 1250.00 | 2 |
| BLAKE | 2850.00 | 4 |
| CLARK | 2450.00 | 4 |
| SCOTT | 3000.00 | 4 |
| KING | 5000.00 | 5 |
| TURNER | 1500.00 | 3 |
| ADAMS | 1100.00 | 1 |
| JAMES | 950.00 | 1 |
| FORD | 3000.00 | 4 |
| MILLER | 1300.00 | 2 |
+--------+---------+-------+
一张表看做两张表
mysql> select e.ename as '员工名',b.ename as '领导名'from emp e join emp b on e.mgr = b.empno;
+--------+--------+
| 员工名 | 领导名 |
+--------+--------+
| SMITH | FORD |
| ALLEN | BLAKE |
| WARD | BLAKE |
| JONES | KING |
| MARTIN | BLAKE |
| BLAKE | KING |
| CLARK | KING |
| SCOTT | JONES |
| TURNER | BLAKE |
| ADAMS | SCOTT |
| JAMES | BLAKE |
| FORD | JONES |
| MILLER | CLARK |
+--------+--------+
mysql> select a.ename '员工',b.ename '领导' from emp b right join emp a on a.mgr=b.empno;
+--------+-------+
| 员工 | 领导 |
+--------+-------+
| SMITH | FORD |
| ALLEN | BLAKE |
| WARD | BLAKE |
| JONES | KING |
| MARTIN | BLAKE |
| BLAKE | KING |
| CLARK | KING |
| SCOTT | JONES |
| KING | NULL |
| TURNER | BLAKE |
| ADAMS | SCOTT |
| JAMES | BLAKE |
| FORD | JONES |
| MILLER | CLARK |
+--------+-------+
mysql> select a.ename '员工',b.ename '领导' from emp a left join emp b on a.mgr=b.empno;
+--------+-------+
| 员工 | 领导 |
+--------+-------+
| SMITH | FORD |
| ALLEN | BLAKE |
| WARD | BLAKE |
| JONES | KING |
| MARTIN | BLAKE |
| BLAKE | KING |
| CLARK | KING |
| SCOTT | JONES |
| KING | NULL |
| TURNER | BLAKE |
| ADAMS | SCOTT |
| JAMES | BLAKE |
| FORD | JONES |
| MILLER | CLARK |
+--------+-------+
mysql> select d.* from emp e right join dept d on e.deptno=d.deptno where e.empno is null;
+--------+------------+--------+
| DEPTNO | DNAME | LOC |
+--------+------------+--------+
| 40 | OPERATIONS | BOSTON |
+--------+------------+--------+
mysql> select e.ename '员工',d.dname,s.grade,e1.ename '领导' from emp e join dept d on e.deptno=d.deptno join salgrade s on e.sal between s.losal and s.hisal left join emp e1 on e.mgr = e1.empno;
+--------+------------+-------+-------+
| 员工 | dname | grade | 领导 |
+--------+------------+-------+-------+
| SMITH | RESEARCH | 1 | FORD |
| ALLEN | SALES | 3 | BLAKE |
| WARD | SALES | 2 | BLAKE |
| JONES | RESEARCH | 4 | KING |
| MARTIN | SALES | 2 | BLAKE |
| BLAKE | SALES | 4 | KING |
| CLARK | ACCOUNTING | 4 | KING |
| SCOTT | RESEARCH | 4 | JONES |
| KING | ACCOUNTING | 5 | NULL |
| TURNER | SALES | 3 | BLAKE |
| ADAMS | RESEARCH | 1 | SCOTT |
| JAMES | SALES | 1 | BLAKE |
| FORD | RESEARCH | 4 | JONES |
| MILLER | ACCOUNTING | 2 | CLARK |
+--------+------------+-------+-------+
mysql> select t.*,s.grade from (select deptno,avg(sal) as avgsal from emp group by deptno) t join salgrade s on t.avgsal between s.losal and s.hisal;
+--------+-------------+-------+
| deptno | avgsal | grade |
+--------+-------------+-------+
| 20 | 2175.000000 | 4 |
| 30 | 1566.666667 | 3 |
| 10 | 2916.666667 | 4 |
+--------+-------------+-------+
mysql> select e.deptno,avg(s.grade) from emp e join salgrade s on e.sal between s.losal and s.hisal group by e.deptno;
+--------+--------------+
| deptno | avg(s.grade) |
+--------+--------------+
| 20 | 2.8000 |
| 30 | 2.5000 |
| 10 | 3.6667 |
+--------+--------------+
mysql> select e.ename,d.dname from emp e join dept d on e.deptno=d.deptno;
mysql> select e.ename,(select d.dname from dept d where e.deptno = d.deptno) as dname from emp e;
+--------+------------+
| ename | dname |
+--------+------------+
| SMITH | RESEARCH |
| ALLEN | SALES |
| WARD | SALES |
| JONES | RESEARCH |
| MARTIN | SALES |
| BLAKE | SALES |
| CLARK | ACCOUNTING |
| SCOTT | RESEARCH |
| KING | ACCOUNTING |
| TURNER | SALES |
| ADAMS | RESEARCH |
| JAMES | SALES |
| FORD | RESEARCH |
| MILLER | ACCOUNTING |
+--------+------------+
mysql> select ename from emp union select dname from dept;
+------------+
| ename |
+------------+
| SMITH |
| ALLEN |
| WARD |
| JONES |
| MARTIN |
| BLAKE |
| CLARK |
| SALES |
| OPERATIONS |
+------------+
每页显示pageSize条记录:第pageNo页:(pageNo - 1)* pageSize,pageSize
mysql> select ename,sal from emp order by sal desc limit 0,5;
+-------+---------+
| ename | sal |
+-------+---------+
| KING | 5000.00 |
| FORD | 3000.00 |
| SCOTT | 3000.00 |
| JONES | 2975.00 |
| BLAKE | 2850.00 |
+-------+---------+
mysql> select ename,sal from emp order by sal desc limit 3,6;
+--------+---------+
| ename | sal |
+--------+---------+
| JONES | 2975.00 |
| BLAKE | 2850.00 |
| CLARK | 2450.00 |
| ALLEN | 1600.00 |
| TURNER | 1500.00 |
| MILLER | 1300.00 |
+--------+---------+
create table t_user(
usercode varchar(255) not null,
username varchar(255)
);
# 多个字段联合添加1个约束unique 【表级约束】
create table t_user(
usercode varchar(255),
username varchar(255),
unique(usercode,username)
);
# 单个字段添加1个约束unique 【列级约束】
create table t_user(
usercode varchar(255) unique,
username varchar(255) unique
);
# 列级约束
create table t_user(
id int primary key,
usercode varchar(255),
username varchar(255)
);
# 表级约束
create table t_user(
id int ,
usercode varchar(255),
username varchar(255),
primary key(id)
);
create table t_user(
id int primary key auto_increment,
username varchar(255)
)
drop table if exists t_student;
drop table if exists t_class;
# 父表
create table t_class(
cno int,
canme varchar(255),
primary key(cno)
);
# 子表
create table t_class(
cno int,
sanme varchar(255),
classno int,
foreign key(classno) references t_class(cno)
);
select @@global.tx_isolation;
start transaction;
set global transaction isolation level read uncommitted;
set global transaction isolation level read committed;
set global transaction isolation level repeatable read;
set global transaction isolation level serializable;
start transaction;
:关闭自动提交机制
rollback
: 回滚事务
commit
: 提交
mysql> explain select ename,sal from emp where sal = 800;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| 1 | SIMPLE | emp | NULL | ALL | NULL | NULL | NULL | NULL | 14 | 10.00 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
create index emp_sal_index on emp(sal);
mysql> explain select ename,sal from emp where sal = 800;
+----+-------------+-------+------------+------+---------------+---------------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+---------------+---------+-------+------+----------+-------+
| 1 | SIMPLE | emp | NULL | ref | emp_sal_index | emp_sal_index | 9 | const | 1 | 100.00 | NULL |
+----+-------------+-------+------------+------+---------------+---------------+---------+-------+------+----------+-------+
create view myview as select empno,ename from emp;
drop view myview;
# 多对多?三张表,关系表两个外键。
t_student学生表
sno(pk) sname
---------------------
1 张三
2 李四
3 王五
t_teacher 讲师表
tno(pk) tname
----------------------
1 王老师
2 张老师
3 李老师
t_student_teacher_relation 学生讲师关系表
id(pk) sno(fk) tno(fk)
-------------------------------------------
1 1 3
2 1 1
3 2 2
4 2 3
5 3 1
6 3 3
建立在第二范式基础上的,非主键字段不能传递依赖于主键字段。(不要产生传递依赖)
学生编号(PK) | 学生姓名 | 班级编号 | 班级名称 |
---|---|---|---|
1001 | 张三 | 01 | 一年一班 |
1002 | 李四 | 02 | 一年二班 |
1003 | 王五 | 03 | 一年三班 |
1004 | 六 | 03 | 一年三班 |
从上表可以看出,班级名称字段存在冗余,因为班级名称字段没有直接依赖于主键,班级名称字段依赖于班级编号,班级编号依赖于学生编号,那么这就是传递依赖,解决的办法是将冗余字段单独拿出来建立表,如:
学生信息表
学生编号(PK) | 学生姓名 | 班级编号(FK) |
---|---|---|
1001 | 张三 | 01 |
1002 | 李四 | 02 |
1003 | 王五 | 03 |
1004 | 六 | 03 |
班级信息表
班级编号(PK) | 班级名称 |
---|---|
01 | 一年一班 |
02 | 一年二班 |
03 | 一年三班 |
以上设计是一种典型的一对多的设计,一存储在一张表中,多存储在一张表中,在多的那张表中添加外键指向一的一方的主键