SQL主要分为三类：
DDL：数据定义语句 数据定义语言 定义不同的数据段，数据表、列、索引等数据库对象 『create drop alter』
DML ：数据操作语句 数据操作语句，用于添加、删除、更新和查询数据库记录 『insert ，delete，update，select』
DCL：数据控制语句 数据控制语句，用于控制不同数据段之间的许可和访问级别的语句，『grant，revoke』
[root@host50 mysql]# mysql -uroot -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g. ------语句以；或者\g结束
Your MySQL connection id is 5 -----------------连接mysql的次数
Server version: 5.7.17 MySQL Community Server (GPL) --------------------mysql的版本信息
DDL语句
mysql> create database zhuhaiyan; ----------创建名称叫zhuhaiyan的数据库
Query OK, 1 row affected (0.01 sec)
mysql> drop database zhuhaiyan; -----------删除名称叫zhuhaiyan的数据库
Query OK, 0 rows affected (0.00 sec)
mysql> create table zhy(name char(4),age int(2)); -----------创建表名称为zhy的表，表中的字段为name，age
Query OK, 0 rows affected (0.72 sec)
mysql> alter table zhy add column sex char(2); --------修改表：向表名为zhy的表插入了字段为sex的字段
Query OK, 0 rows affected (0.47 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> alter table zhy drop column age; ---------修改表：在表名为zhy删除字段为age的列
Query OK, 0 rows affected (0.46 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> alter table zhy add age int(2) after name; -------修改表：在表中添加age的字段，并追加到name字段后
Query OK, 0 rows affected (1.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> alter table zhy modify age int(2) first; -----修改表：把age字段放在第一列
Query OK, 0 rows affected (0.62 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> alter table zhy modify name char(6); -----修改表中的字段的宽度
mysql> drop table zhy ; -------删除名为zhy的表
Query OK, 0 rows affected (0.11 sec)
mysql> alter user root@"localhost" identified by "123456"; -------修改用户的密码
Query OK, 0 rows affected (0.00 sec)
mysql> alter table 学生信息表 rename student; -----更加表的名称
Query OK, 0 rows affected (0.22 sec)
mysql> alter table zhy change sex sex1 char(3); --------修改表的的字段名，把字段为sex改成sex1
Query OK, 0 rows affected (0.91 sec)
Records: 0 Duplicates: 0 Warnings: 0
DML语句
mysql> insert into zhy value(11,'zhu','nv'); ---------向表zhy中插入数据
Query OK, 1 row affected (0.04 sec)
mysql> insert into zhy(age,name,sex1) value(12,'hai','man'); ---------向表zhy中插入数据
Query OK, 1 row affected (0.05 sec)
mysql> insert into zhy(age,name) values(13,'hz'),(15,'ss'); ---------向表zhy中插入数据
Query OK, 2 rows affected (0.10 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> update zhy set name='yan' where age=12; ---------单表更新数据
Query OK, 2 rows affected (0.09 sec)
Rows matched: 2 Changed: 2 Warnings: 0
mysql> update emp a,dept b set a.sal=a.sal*b.deptno,b.deptname=a.ename where a.deptno=b.deptno; ---------单表更新数据
mysql> delete a,b from emp a,dept b where a.deptno=b.deptno and a.deptno=3; ---------删除表中的数据
Query OK, 2 rows affected (0.13 sec)
mysql> select distinct deptno from emp; -------查询表中的数据，加distinct是表示不显示重复数据
2 rows in set (0.00 sec)
mysql> select * from emp where deptno>1; -------条件查找，值大于1的则显示
1 row in set (0.00 sec)
mysql> select * from emp order by deptno; -------排序查询，默认是升序查询
4 rows in set (0.00 sec)
mysql> select * from emp order by deptno desc; ---------排序查询，降序查询
4 rows in set (0.00 sec)
mysql> select * from emp order by sa1 limit 2; -------只显示前两行
mysql> select * from emp order by sa1 limit 1,2; -----显示1行后的2行
mysql> select count(1) from emp; --------统计emp的行数
mysql> select deptno,count(1) from emp group by deptno; -------在部门的条件统计人数
mysql> select deptno,count(1) from emp group by deptno with rollup; -----统计部门人数和总人数
mysql> select deptno,count(1) from emp group by deptno having count(1)>1; ----统计部门人数大于1
mysql> select sum(sa1),max(sa1),min(sa1) from emp; ----统计公司所有员工的薪水、最高和最底薪水
select ename,deptname from dept right join emp on dept.deptno=emp.deptno; -----右连接查询
select ename,deptname from emp left join dept on dept.deptno=emp.deptno; ------左连接查询
mysql> select * from emp where deptno in(select deptno from dept); ------子查询
mysql> select deptno from emp union select deptno from dept; ------联合查询（union all 显示重复的数）
DCL语句
mysql> grant select,insert on zhuhaiyan.* to 'zhu'@'localhost' identified by '654321';
Query OK, 0 rows affected, 1 warning (0.00 sec)
-------将数据库zhuhaiyan的查询和插入权限给用户zhu，用户zhu的登录权限为654321
mysql> revoke select on zhuhaiyan.* from 'zhu'@'localhost';
Query OK, 0 rows affected (0.00 sec)
-------将数据库zhuhaiyan的查询权限从用户zhu收回