MYSQL——表记录相关操作（ 单表查询）

一、表记录相关操作

　　增加记录
　　修改记录
　　删除记录

　　查询记录（单表查询，多表联合）

　　单表查询语法(一定要注意执行顺序！)
　　select distinct 字段1,字段2,字段3,... from 表名
                            where 过滤条件
                            group by 分组的条件
                            having 筛选条件
                            order by 排序字段
                            limit n;

# 插入
mysql> create table user(name varchar(16),password varchar(10));
Query OK, 0 rows affected (0.29 sec)
mysql>
mysql> insert into user select user,password from mysql.user;

# 删除
delete from 表 where 条件;

# 更新
update 表 set 字段=值 where 条件;

# 单表查询语法
select distinct 字段1,字段2,字段3,... from 表名
                            where 过滤条件
                            group by 分组的条件
                            having 筛选条件
                            order by 排序字段
                            limit n;


# 简单查询
select name,sex from emp;
select name as 名字,sex 性别 from emp;

select * from emp;

# 避免重复（针对的是记录）
select distinct post from emp;

# 进行四则运算
select name as 名字,salary*12 as 年薪 from emp;

# concat()拼接记录的内容
select name ,concat(salary*12,"$") from emp;
select name ,concat("annual_salary",':',salary*12) as 年薪 from emp;
select name ,concat("annual_salary",':',salary*12,':','$') as 年薪 from emp;
select name ,concat_ws(":","annual_salary",salary*12,'$') as 年薪 from emp;



select (
    case
    when name="egon" then
        name
    when name="alex" then
        concat(name,"_dsb")
    else
        concat(name,"_sb")
    end
) as 名字 from emp;


===========================================where
select * from emp where id >= 3 and id <= 5;
select * from emp where id between 3 and 5;
select * from emp where id not between 3 and 5;

select * from emp where id=3 or id=5 or id=7;
select * from emp where id in (3,5,7);
select * from emp where id not in (3,5,7);

select * from emp where id=3 or id=5 or id=7;


select * from emp where name like 'jin%';
select * from emp where name like 'jin___';

select * from emp where name regexp 'n$';


mysql> select * from emp where post_comment is not null;
Empty set (0.00 sec)

mysql> update emp set post_comment='' where id=3;
Query OK, 1 row affected (0.07 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from emp where post_comment is not null;
+----+---------+------+-----+------------+---------+--------------+---------+--------+-----------+
| id | name    | sex  | age | hire_date  | post    | post_comment | salary  | office | depart_id |
+----+---------+------+-----+------------+---------+--------------+---------+--------+-----------+
|  3 | wupeiqi | male |  81 | 2013-03-05 | teacher |              | 8300.00 |    401 |         1 |
+----+---------+------+-----+------------+---------+--------------+---------+--------+-----------+
1 row in set (0.00 sec)

mysql>



select * from emp where name="丫丫";
select * from emp where name regexp "丫$";
select * from emp where name like "丫_";
select * from emp where name regexp "^程";
select hex(name) from t4  where hex(name) regexp 'e[4-9][0-9a-f]{4}';



===========================================group by
分完组之后只能看到分组的字段以及聚合的结果

max()
min()
avg()
sum()
count()

select depart_id,count(id),avg(salary),max(age),min(salary),sum(salary) from emp group by depart_id;

# 每个部门都有多少个人
select depart_id,count(id) from emp group by depart_id;

# 每个职位男生的平均薪资
select post,avg(salary) from emp where sex="male" group by post;


select post, group_concat(name) from emp group by post;
select post, group_concat(name) from emp where sex="male" group by post;

===========================================having
# having与where本质区别就是在于having是在分组之后发生过滤，可以使用聚合函数

mysql> select max(salary) from emp where max(salary) > 100000;
ERROR 1111 (HY000): Invalid use of group function
mysql> select max(salary) from emp having max(salary) > 100000;
+-------------+
| max(salary) |
+-------------+
|  1000000.31 |
+-------------+
1 row in set (0.00 sec)

mysql>



# 找出来男生平均薪资大于3000的职位

select post,avg(salary) from emp where sex="male" group by post having avg(salary) > 8000;



===========================================order by排序
select * from emp order by salary;
 select * from emp order by salary desc;
 select * from emp order by age,id desc;
ps:asc升序（默认为升序，一般就不要写了） 
　　desc降序
 select post,avg(salary) from emp where sex="male" group by post having avg(salary) > 3000;
 mysql> select post,avg(salary) from emp where sex="male" group by post having avg(salary) > 3000;
+-----------------------------------------+---------------+
| post                                    | avg(salary)   |
+-----------------------------------------+---------------+
| operation                               |  16000.043333 |
| teacher                                 | 175650.051667 |
| xxxxxxxxx驻沙河办事处外交大使              |   7300.330000 |
+-----------------------------------------+---------------+
3 rows in set (0.00 sec)

mysql> select post,avg(salary) from emp where sex="male" group by post having avg(salary) > 3000 order by avg(salary);
+-----------------------------------------+---------------+
| post                                    | avg(salary)   |
+-----------------------------------------+---------------+
| xxxxxxxxx驻沙河办事处外交大使              |   7300.330000 |
| operation                               |  16000.043333 |
| teacher                                 | 175650.051667 |
+-----------------------------------------+---------------+
3 rows in set (0.00 sec)

mysql> select post,avg(salary) as v from emp where sex="male" group by post having avg(salary) > 3000 order by v;
+-----------------------------------------+---------------+
| post                                    | v             |
+-----------------------------------------+---------------+
| xxxxxxxxx驻沙河办事处外交大使              |   7300.330000 |
| operation                               |  16000.043333 |
| teacher                                 | 175650.051667 |
+-----------------------------------------+---------------+
3 rows in set (0.00 sec)

mysql>


分页显示：（比如淘宝里商品页面显示，可以分好多页）
select * from emp limit 0,5;
select * from emp limit 5,5;
select * from emp limit 10,5;
select * from emp limit 15,5;
select * from emp limit 20,5;

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