单表查询

Posted 2021-03-26 inmeditation

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准备工作

准备表company.employee5

mysql> create database company;
Query OK, 1 row affected (0.00 sec)

mysql> use company;
Database changed
mysql> create table company.employee5(
    -> id int primary key auto_increment not null,
    -> name varchar(30) not null,
    -> sex enum('male','female') default 'male' not null,
    -> hire_date date not null,
    -> post varchar(50) not null,
    -> job_description varchar(100),
    -> salary double(15,2) not null,
    -> office int,
    -> dep_id int
    -> );
Query OK, 0 rows affected (0.24 sec)

插入数据

mysql> insert into company.employee5(name,sex,hire_date,post,job_description,salary,office,dep_id) value
    ->    ('jack','male','20180202','instructor','teach',5000,501,100),
    ->    ('tom','male','20180203','instructor','teach',5000,501,100),
    ->    ('robin','male','20180202','instructor','teach',8000,501,100),
    ->    ('alice','female','20180202','instructor','teach',7200,501,100),
    ->    ('tianyun','male','20180202','instructor','teach',600,502,100),
    ->    ('harry','male','20180202','hr',NULL,6000,502,101),
    ->    ('emma','female','20180206','sale','salecc',20000,503,102),
    ->    ('christine','female','20180205','sale',NULL,2200,503,102),
    ->    ('zhuzhu','male','20180205','sale',NULL,2200,503,102),
    ->    ('gougou','male','20180205','sale','',2200,503,102);
Query OK, 10 rows affected (0.01 sec)
Records: 10  Duplicates: 0  Warnings: 0

简单查询

查询表全部内容

mysql> select * from employee5;                                                                                                      
+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+
| id | name      | sex    | hire_date  | post       | job_description | salary   | office | dep_id |
+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+
|  2 | jack      | male   | 2018-02-02 | instructor | teach           |  5000.00 |    501 |    100 |
|  3 | tom       | male   | 2018-02-03 | instructor | teach           |  5000.00 |    501 |    100 |
|  4 | robin     | male   | 2018-02-02 | instructor | teach           |  8000.00 |    501 |    100 |
|  5 | alice     | female | 2018-02-02 | instructor | teach           |  7200.00 |    501 |    100 |
|  6 | tianyun   | male   | 2018-02-02 | instructor | teach           |   600.00 |    502 |    100 |
|  7 | harry     | male   | 2018-02-02 | hr         | NULL            |  6000.00 |    502 |    101 |
|  8 | emma      | female | 2018-02-06 | sale       | salecc          | 20000.00 |    503 |    102 |
|  9 | christine | female | 2018-02-05 | sale       | NULL            |  2200.00 |    503 |    102 |
| 10 | zhuzhu    | male   | 2018-02-05 | sale       | NULL            |  2200.00 |    503 |    102 |
| 11 | gougou    | male   | 2018-02-05 | sale       |                 |  2200.00 |    503 |    102 |
+----+-----------+--------+------------+------------+-----------------+----------+--------+--------+
10 rows in set (0.00 sec)

查询表的某几个字段

mysql> select name,post,salary from employee5;
+-----------+------------+----------+
| name      | post       | salary   |
+-----------+------------+----------+
| jack      | instructor |  5000.00 |
| tom       | instructor |  5000.00 |
| robin     | instructor |  8000.00 |
| alice     | instructor |  7200.00 |
| tianyun   | instructor |   600.00 |
| harry     | hr         |  6000.00 |
| emma      | sale       | 20000.00 |
| christine | sale       |  2200.00 |
| zhuzhu    | sale       |  2200.00 |
| gougou    | sale       |  2200.00 |
+-----------+------------+----------+
10 rows in set (0.00 sec)

去重,仅用于单一字段

mysql> select distinct post from employee5;
+------------+
| post       |
+------------+
| instructor |
| hr         |
| sale       |
+------------+
3 rows in set (0.00 sec)

计算出每个员工的年薪(14薪)

mysql> select name,salary,salary*14 from employee5;
+-----------+----------+-----------+
| name      | salary   | salary*14 |
+-----------+----------+-----------+
| jack      |  5000.00 |  70000.00 |
| tom       |  5000.00 |  70000.00 |
| robin     |  8000.00 | 112000.00 |
| alice     |  7200.00 | 100800.00 |
| tianyun   |   600.00 |   8400.00 |
| harry     |  6000.00 |  84000.00 |
| emma      | 20000.00 | 280000.00 |
| christine |  2200.00 |  30800.00 |
| zhuzhu    |  2200.00 |  30800.00 |
| gougou    |  2200.00 |  30800.00 |
+-----------+----------+-----------+
10 rows in set (0.00 sec)

显示别名,将salary*14显示为annual_salary

mysql> select name,salary,salary*14 as annual_salary from employee5;
+-----------+----------+---------------+
| name      | salary   | annual_salary |
+-----------+----------+---------------+
| jack      |  5000.00 |      70000.00 |
| tom       |  5000.00 |      70000.00 |
| robin     |  8000.00 |     112000.00 |
| alice     |  7200.00 |     100800.00 |
| tianyun   |   600.00 |       8400.00 |
| harry     |  6000.00 |      84000.00 |
| emma      | 20000.00 |     280000.00 |
| christine |  2200.00 |      30800.00 |
| zhuzhu    |  2200.00 |      30800.00 |
| gougou    |  2200.00 |      30800.00 |
+-----------+----------+---------------+
10 rows in set (0.00 sec)

定义显示格式

CONCAT()函数用来连接字符串

mysql> select concat(name,' annual salary:  ',salary*14) as Annual_salary from employee5;
+------------------------------------+
| Annual_salary                      |
+------------------------------------+
| jack annual salary:  70000.00      |
| tom annual salary:  70000.00       |
| robin annual salary:  112000.00    |
| alice annual salary:  100800.00    |
| tianyun annual salary:  8400.00    |
| harry annual salary:  84000.00     |
| emma annual salary:  280000.00     |
| christine annual salary:  30800.00 |
| zhuzhu annual salary:  30800.00    |
| gougou annual salary:  30800.00    |
+------------------------------------+
10 rows in set (0.00 sec)

2条件查询

单条件查询

查询职位是hr的员工

mysql> select name,post from employee5 where post='hr';
+-------+------+
| name  | post |
+-------+------+
| harry | hr   |
+-------+------+
1 row in set (0.00 sec)

多条件查询

查看职位是"sale销售"的员工,但是薪水少于等于5000

mysql> select name,post,salary from employee5 where post='sale' and salary<=5000;
+-----------+------+---------+
| name      | post | salary  |
+-----------+------+---------+
| christine | sale | 2200.00 |
| zhuzhu    | sale | 2200.00 |
| gougou    | sale | 2200.00 |
+-----------+------+---------+
3 rows in set (0.00 sec)

关键字between and 和 not between and

查看工资5000~10000范围内的员工

mysql> select name,salary from employee5 where salary between 5000 and 10000;
+-------+---------+
| name  | salary  |
+-------+---------+
| jack  | 5000.00 |
| tom   | 5000.00 |
| robin | 8000.00 |
| alice | 7200.00 |
| harry | 6000.00 |
+-------+---------+
5 rows in set (0.00 sec)

查看不是这个范围的员工

mysql> select name,salary from employee5 where salary not between 5000 and 10000;
+-----------+----------+
| name      | salary   |
+-----------+----------+
| tianyun   |   600.00 |
| emma      | 20000.00 |
| christine |  2200.00 |
| zhuzhu    |  2200.00 |
| gougou    |  2200.00 |
+-----------+----------+
5 rows in set (0.00 sec)

关键字is null和is not null

空和非空

查看job_description职位描述字段为空的员工

mysql> select name,job_description from employee5 where job_description is null;
+-----------+-----------------+
| name      | job_description |
+-----------+-----------------+
| harry     | NULL            |
| christine | NULL            |
| zhuzhu    | NULL            |
+-----------+-----------------+
3 rows in set (0.00 sec)

查看job_description职位描述字段不为空的员工

mysql> select name,job_description from employee5 where job_description is not null;
+---------+-----------------+
| name    | job_description |
+---------+-----------------+
| jack    | teach           |
| tom     | teach           |
| robin   | teach           |
| alice   | teach           |
| tianyun | teach           |
| emma    | salecc          |
| gougou  |                 |
+---------+-----------------+
7 rows in set (0.00 sec)

集合查询 in和not in

mysql> select name,salary from employee5 where salary=2000 or salary=5000 or salary=6000 or salary=20000;
+-------+----------+
| name  | salary   |
+-------+----------+
| jack  |  5000.00 |
| tom   |  5000.00 |
| harry |  6000.00 |
| emma  | 20000.00 |
+-------+----------+
4 rows in set (0.00 sec)

mysql> select name,salary from employee5 where salary in (2000,5000,6000,20000);
+-------+----------+
| name  | salary   |
+-------+----------+
| jack  |  5000.00 |
| tom   |  5000.00 |
| harry |  6000.00 |
| emma  | 20000.00 |
+-------+----------+
4 rows in set (0.00 sec)

mysql> select name,salary from employee5 where salary not in (2000,5000,6000,20000);
+-----------+---------+
| name      | salary  |
+-----------+---------+
| robin     | 8000.00 |
| alice     | 7200.00 |
| tianyun   |  600.00 |
| christine | 2200.00 |
| zhuzhu    | 2200.00 |
| gougou    | 2200.00 |
+-----------+---------+
6 rows in set (0.00 sec)

模糊查询

% ---- 任意多个字符
_ ---- 任意单个字符

mysql> select name from employee5 where name like 'al%';
+-------+
| name  |
+-------+
| alice |
+-------+
1 row in set (0.00 sec)

mysql> select name from employee5 where name like 'al_';
Empty set (0.00 sec)

mysql> select name from employee5 where name like 'al___';
+-------+
| name  |
+-------+
| alice |
+-------+
1 row in set (0.00 sec)

3排序

单列排序

默认使用asc ,升序从小到大

mysql> select name,salary from employee5 order by salary;
+-----------+----------+
| name      | salary   |
+-----------+----------+
| tianyun   |   600.00 |
| christine |  2200.00 |
| zhuzhu    |  2200.00 |
| gougou    |  2200.00 |
| jack      |  5000.00 |
| tom       |  5000.00 |
| harry     |  6000.00 |
| alice     |  7200.00 |
| robin     |  8000.00 |
| emma      | 20000.00 |
+-----------+----------+
10 rows in set (0.00 sec)

降序从大到小,需要指定为desc

mysql> select name,salary from employee5 order by salary desc;
+-----------+----------+
| name      | salary   |
+-----------+----------+
| emma      | 20000.00 |
| robin     |  8000.00 |
| alice     |  7200.00 |
| harry     |  6000.00 |
| jack      |  5000.00 |
| tom       |  5000.00 |
| christine |  2200.00 |
| zhuzhu    |  2200.00 |
| gougou    |  2200.00 |
| tianyun   |   600.00 |
+-----------+----------+
10 rows in set (0.00 sec)

多列排序

先按入职时间降序,再按薪资升序

mysql> mysql> select name,hire_date,salary from employee5 order by hire_date desc, salary;
+-----------+------------+----------+
| name      | hire_date  | salary   |
+-----------+------------+----------+
| emma      | 2018-02-06 | 20000.00 |
| christine | 2018-02-05 |  2200.00 |
| zhuzhu    | 2018-02-05 |  2200.00 |
| gougou    | 2018-02-05 |  2200.00 |
| tom       | 2018-02-03 |  5000.00 |
| tianyun   | 2018-02-02 |   600.00 |
| jack      | 2018-02-02 |  5000.00 |
| harry     | 2018-02-02 |  6000.00 |
| alice     | 2018-02-02 |  7200.00 |
| robin     | 2018-02-02 |  8000.00 |
+-----------+------------+----------+
10 rows in set (0.00 sec)

4限制查询的记录数

只显示排序后公司薪资最高的前5位员工

从0开始查询,共查询5条

mysql> mysql> select name,salary from employee5 order by salary desc limit 0,5;
+-------+----------+
| name  | salary   |
+-------+----------+
| emma  | 20000.00 |
| robin |  8000.00 |
| alice |  7200.00 |
| harry |  6000.00 |
| jack  |  5000.00 |
+-------+----------+
5 rows in set (0.00 sec)

5使用集合函数查询

函数	描述
count()	统计数量
max()	最大值
min	最小值
avg	平均值
sum	总和值

mysql> select count(*) from employee5;
+----------+
| count(*) |
+----------+
|       10 |
+----------+
1 row in set (0.00 sec)

mysql> select count(*) from employee5 where post='hr' ;
+----------+
| count(*) |
+----------+
|        1 |
+----------+
1 row in set (0.00 sec)

mysql> select max(salary) from employee5;
+-------------+
| max(salary) |
+-------------+
|    20000.00 |
+-------------+
1 row in set (0.00 sec)
mysql> select max(salary) from employee5 where job_description='teach';
+-------------+
| max(salary) |
+-------------+
|     8000.00 |
+-------------+
1 row in set (0.00 sec)

mysql> select min(salary) from employee5 where job_description='teach';
+-------------+
| min(salary) |
+-------------+
|      600.00 |
+-------------+
1 row in set (0.00 sec)

mysql> select avg(salary) from employee5;
+-------------+
| avg(salary) |
+-------------+
| 5840.000000 |
+-------------+
1 row in set (0.00 sec)
mysql> select avg(salary) from employee5 where job_description='teach';
+-------------+
| avg(salary) |
+-------------+
| 5160.000000 |
+-------------+
1 row in set (0.00 sec)

mysql> select sum(salary) from employee5;
+-------------+
| sum(salary) |
+-------------+
|    58400.00 |
+-------------+
1 row in set (0.00 sec)

6分组查询

group_concat()函数和group by()函数通常一块使用

按照部门来分组

mysql> mysql> select post,group_concat(name) from employee5 group by post;
+------------+------------------------------+
| post       | group_concat(name)           |
+------------+------------------------------+
| hr         | harry                        |
| instructor | jack,tom,robin,alice,tianyun |
| sale       | emma,christine,zhuzhu,gougou |
+------------+------------------------------+
3 rows in set (0.00 sec)

mysql> select post,group_concat(salary) from employee5 group by post;
+------------+----------------------------------------+
| post       | group_concat(salary)                   |
+------------+----------------------------------------+
| hr         | 6000.00                                |
| instructor | 5000.00,5000.00,8000.00,7200.00,600.00 |
| sale       | 20000.00,2200.00,2200.00,2200.00       |
+------------+----------------------------------------+
3 rows in set (0.00 sec)

group by()函数和集合函数一起使用

mysql> select post,sum(salary),avg(salary),count(*) from employee5 group by post;
+------------+-------------+-------------+----------+
| post       | sum(salary) | avg(salary) | count(*) |
+------------+-------------+-------------+----------+
| hr         |     6000.00 | 6000.000000 |        1 |
| instructor |    25800.00 | 5160.000000 |        5 |
| sale       |    26600.00 | 6650.000000 |        4 |
+------------+-------------+-------------+----------+
3 rows in set (0.00 sec)

7正则表达式查询

‘^ali‘-----以ali开头
‘yun$‘----以yun结尾
‘m{2}‘----m出现的次数

mysql> select name,salary from employee5 where name regexp 'm{2}';
+------+----------+
| name | salary   |
+------+----------+
| emma | 20000.00 |
+------+----------+
1 row in set (0.00 sec)

小结

对字符串匹配的方式

where name = 'tom';
where name like 'to%';
where name regexp 'yun$';

补充:嵌套查询

mysql> mysql> select * from employee5 where salary = (select max(salary) from employee5);
+----+------+--------+------------+------+-----------------+----------+--------+--------+
| id | name | sex    | hire_date  | post | job_description | salary   | office | dep_id |
+----+------+--------+------------+------+-----------------+----------+--------+--------+
|  8 | emma | female | 2018-02-06 | sale | salecc          | 20000.00 |    503 |    102 |
+----+------+--------+------------+------+-----------------+----------+--------+--------+
1 row in set (0.00 sec)

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