增:

insert into 表名 (列名1, 列名2,) values(值1, 值2);

insert into 表名 (列名1, 列名2,) values(值1, 值2),(值1,值2),(值n,值n);

insert into 表名 (列名1, 列名2,) select 列名1, 列名2 from 表名;

删除:

delete from 表名;

delete from 表名 where id > 10

delete from 表名 where id < 10

delete from 表名 where id <= 10

delete from 表名 where id >= 10

delete from 表名 where id != 10

delete from 表名 where id = 10 and name='xxx';  and : 并且 两个条件都必须要成立

delete from 表名 where id = 10 or name='xxx';   or :  或者 只要满足一个条件成立

修改:

update 表名  set name='zekai', age=23 where id > 10;

查询:

基本:

select * from 表名;

select name , age from 表名;

高级:

a. where 条件查询:

select * from 表名 where  id=10;

select * from 表名 where  id >10 and id<15;

select * from 表名 where  id > 10;

!= : 不等于

between and:       between是一个闭区间

select * from t4 where id between 9 and 12;

in: 在某一个集合中

select * from t4 where id in (9,10,11....);

select * from t4 where id in (select id from t3 where id between 2 and 4)

b. 通配符:

alex

select * from 表 where name like 'ale%'  - ale开头的所有(多个字符串)

select * from 表 where name like 'ale_'  - ale开头的所有(一个字符)

c.     限制取几条:

select * from 表名 limit 索引偏移量, 取出多少条数据;

select * from t3 limit 0, 10;  第一页

select * from t3 limit 10, 10;  第二页

page = input('page:')

page    索引偏移量      数据量(offset)

1         0              10

2         10             10

3         20             10

4         30             10

page   (page-1)*offset   offset

分页核心SQL:

select * from t3 limit (page-1)*offset, offset;

d.  排序:

order by

降序:

select * from t4 order by 列名 desc; descending

升序:

select * from t4 order by 列名 asc; ascending

多列:

create table t7(

id int auto_increment primary key,

num int not null default 0,

age int not null default 0

)charset=utf8;

insert into t7 (num, age) values (2, 12),(3,13),(4, 12);

select * from t4 order by num desc, name asc;

如果前一列的值相等的话, 会按照后一列的值进行进一步的排序.

e.  分组

select age, 聚合函数(count(num)/sum(num)/max(num)/min(num)/avg(num)) from 表名 group 　　　　　　　　by 列名;

select age, avg(num) from t7 group by age;

select age, count(num) from t7 group by age;

select age, count(num) as cnt from t7 group by age;  显示别名 as

having的二次删选:

select age, count(num) as cnt from t7 group by age  having cnt>1;

where 和 having的区别:

1). having与where类似,可筛选数据

2). where针对表中的列发挥作用,查询数据

3). having针对查询结果中的列发挥作用,二次筛选数据, 和group by配合使用

f.  连表操作

select * from userinfo, department; (笛卡尔积)

select * from userinfo, department where userinfo.depart_id=department.id;

左连接:

select * from userinfo left join department on userinfo.depart_id=department.id;

左边的表全部显示, 右边没有用到不显示

右连接:

select * from userinfo right join department on userinfo.depart_id=department.id;

右边的表全部显示, 左边没关联的用null表示

内连接:

左右两边的数据都会显示

ps:

a.只需要记住左连接 left join

b.可以连接多张表 通过某一个特定的条件

注意查询的顺序:

select name,sum(score) from 表 where id > 10 group by score having age> 12  order by age desc 　　　　　　limit 2, 10