数据库之表的查询

一.新建表：

		mysql> create table t_worker(-> department_id int(11) not null comment'部门号',-> worker_id int(11) primary key not null comment'职工号',-> worker_date date not null comment'工作时间',-> wages float(8,2) not null comment'工资',-> politics varchar(10) not null default '群众'comment '政治面貌',-> name varchar(20) not null comment'姓名',-> borth_date date not null comment '出生日期');
Query OK, 0 rows affected, 3 warnings (0.03 sec)

二.查询表的结构：

mysql> desc t_worker;
+---------------+-------------+------+-----+---------+-------+
| Field         | Type        | Null | Key | Default | Extra |
+---------------+-------------+------+-----+---------+-------+
| department_id | int         | NO   |     | NULL    |       |
| worker_id     | int         | NO   | PRI | NULL    |       |
| worker_date   | date        | NO   |     | NULL    |       |
| wages         | float(8,2)  | NO   |     | NULL    |       |
| politics      | varchar(10) | NO   |     | 群众    |       |
| name          | varchar(20) | NO   |     | NULL    |       |
| borth_date    | date        | NO   |     | NULL    |       |
+---------------+-------------+------+-----+---------+-------+
7 rows in set (0.00 sec)

三.在表里面插入数据：

 insert into t_worker values(101,1001,'2015-5-4',7500.00,'群众','张春燕','1990-7-1');
Query OK, 1 row affected (0.01 sec)mysql> insert into t_worker values(101,1002,'2019-2-6',5200.00,'团员','李明博','1997-2-8');
Query OK, 1 row affected (0.00 sec)mysql> insert into t_worker values(102,1003,'2008-1-4',10500.00,'党员','王博涵','1983-6-8');
Query OK, 1 row affected (0.00 sec)mysql> insert into t_worker values(102,1004,'2016-10-10',5500.00,'群众','赵小军','1994-9-5');
Query OK, 1 row affected (0.00 sec)mysql> insert into t_worker values(102,1005,'2014-4-1',8800.00,'党员','钱有财','1992-9-2');
Query OK, 1 row affected (0.00 sec)mysql> insert into t_worker values(103,1006,'2019-5-5',5500.00,'党员','孙菲菲','1996-9-2');
Query OK, 1 row affected (0.00 sec)

四.查询表中的数据：

mysql> select * from t_worker;
+---------------+-----------+-------------+----------+----------+--------+------------+
| department_id | worker_id | worker_date | wages    | politics | name   | borth_date |
+---------------+-----------+-------------+----------+----------+--------+------------+
|           101 |      1001 | 2015-05-04  |  7500.00 | 群众     | 张春燕 | 1990-07-01 |
|           101 |      1002 | 2019-02-06  |  5200.00 | 团员     | 李明博 | 1997-02-08 |
|           102 |      1003 | 2008-01-04  | 10500.00 | 党员     | 王博涵 | 1983-06-08 |
|           102 |      1004 | 2016-10-10  |  5500.00 | 群众     | 赵小军 | 1994-09-05 |
|           102 |      1005 | 2014-04-01  |  8800.00 | 党员     | 钱有财 | 1992-09-02 |
|           103 |      1006 | 2019-05-05  |  5500.00 | 党员     | 孙菲菲 | 1996-09-02 |
+---------------+-----------+-------------+----------+----------+--------+------------+
6 rows in set (0.00 sec)

题目：
1.显示所有职工的基本信息：

mysql> select * from t_worker;
+---------------+-----------+-------------+----------+----------+--------+------------+
| department_id | worker_id | worker_date | wages    | politics | name   | borth_date |
+---------------+-----------+-------------+----------+----------+--------+------------+
|           101 |      1001 | 2015-05-04  |  7500.00 | 群众     | 张春燕 | 1990-07-01 |
|           101 |      1002 | 2019-02-06  |  5200.00 | 团员     | 李明博 | 1997-02-08 |
|           102 |      1003 | 2008-01-04  | 10500.00 | 党员     | 王博涵 | 1983-06-08 |
|           102 |      1004 | 2016-10-10  |  5500.00 | 群众     | 赵小军 | 1994-09-05 |
|           102 |      1005 | 2014-04-01  |  8800.00 | 党员     | 钱有财 | 1992-09-02 |
|           103 |      1006 | 2019-05-05  |  5500.00 | 党员     | 孙菲菲 | 1996-09-02 |
+---------------+-----------+-------------+----------+----------+--------+------------+
6 rows in set (0.00 sec)

2.查询所有职工所属部门的部门号，不显示重复的部门号：

mysql> select distinct department_id from t_worker;
+---------------+
| department_id |
+---------------+
|           101 |
|           102 |
|           103 |
+---------------+
3 rows in set (0.00 sec)

3.求出所有职工的人数：

mysql> select count(1) from t_worker;
+----------+
| count(1) |
+----------+
|        6 |
+----------+
1 row in set (0.00 sec)

4.列出最高和最低工资：

mysql> select max(wages),min(wages) from t_worker;
+------------+------------+
| max(wages) | min(wages) |
+------------+------------+
|   10500.00 |    5200.00 |
+------------+------------+
1 row in set (0.00 sec)

5.列出职工的平均工资和总工资：

mysql> select round(avg(wages),2) '平均工资值',sum(wages) '总工资' from t_worker;
+------------+----------+
| 平均工资值 | 总工资   |
+------------+----------+
|    7166.67 | 43000.00 |
+------------+----------+
1 row in set (0.00 sec)

6.创建一个只有职工号，姓名，和参加工作的新表，名为工作日期表

mysql> create table work_date_t(-> worker_id varchar(20),-> name varchar(10),-> politices varchar(15));
Query OK, 0 rows affected (0.01 sec)mysql> desc work_date_t;
+-----------+-------------+------+-----+---------+-------+
| Field     | Type        | Null | Key | Default | Extra |
+-----------+-------------+------+-----+---------+-------+
| worker_id | varchar(20) | YES  |     | NULL    |       |
| name      | varchar(10) | YES  |     | NULL    |       |
| politices | varchar(15) | YES  |     | NULL    |       |
+-----------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

7.显示所有党员的年龄:

mysql> select worker_id ,name ,timestampdiff(year,borth_date,curdate()) as 'now age' from t_worker-> where politics='党员';
+-----------+--------+---------+
| worker_id | name   | now age |
+-----------+--------+---------+
|      1003 | 王博涵 |      41 |
|      1005 | 钱有财 |      31 |
|      1006 | 孙菲菲 |      27 |
+-----------+--------+---------+
3 rows in set (0.00 sec)

8.列出工资在4000-8000之间的所有职工姓名：```powershell
mysql> select name from t_worker where wages >4000 and wages <8000 ;
+--------+
| name   |
+--------+
| 张春燕 |
| 李明博 |
| 赵小军 |
| 孙菲菲 |
+--------+
4 rows in set (0.00 sec)

9.列出所有孙姓和李姓的职工姓名：

mysql> select name from t_worker where name like '孙%' or name like '李%';
+--------+
| name   |
+--------+
| 李明博 |
| 孙菲菲 |
+--------+
2 rows in set (0.00 sec)

10，列出所有部门号为102和103且不是党员的职工号，姓名 ：

mysql> select worker_id ,name from t_worker-> where department_id in(102,103)-> and politics!='党员';
+-----------+--------+
| worker_id | name   |
+-----------+--------+
|      1004 | 赵小军 |
+-----------+--------+
1 row in set (0.00 sec)

11.将职工表t_worker中的职工按出生的先后顺序排序：

mysql> select * from t_worker  order by borth_date;
+---------------+-----------+-------------+----------+----------+--------+------------+
| department_id | worker_id | worker_date | wages    | politics | name   | borth_date |
+---------------+-----------+-------------+----------+----------+--------+------------+
|           102 |      1003 | 2008-01-04  | 10500.00 | 党员     | 王博涵 | 1983-06-08 |
|           101 |      1001 | 2015-05-04  |  7500.00 | 群众     | 张春燕 | 1990-07-01 |
|           102 |      1005 | 2014-04-01  |  8800.00 | 党员     | 钱有财 | 1992-09-02 |
|           102 |      1004 | 2016-10-10  |  5500.00 | 群众     | 赵小军 | 1994-09-05 |
|           103 |      1006 | 2019-05-05  |  5500.00 | 党员     | 孙菲菲 | 1996-09-02 |
|           101 |      1002 | 2019-02-06  |  5200.00 | 团员     | 李明博 | 1997-02-08 |
+---------------+-----------+-------------+----------+----------+--------+------------+
6 rows in set (0.00 sec)

12.显示工资最高的前三名职工的职工号与姓名：

mysql> select worker_id , name from t_worker order by  wages desc limit 3;
+-----------+--------+
| worker_id | name   |
+-----------+--------+
|      1003 | 王博涵 |
|      1005 | 钱有财 |
|      1001 | 张春燕 |
+-----------+--------+

3 rows in set (0.00 sec)
13.求出各个部门党员的人数：

mysql> select department_id,count(1) as '党员人数' from t_worker-> where politics = '党员' group by department_id;
+---------------+----------+
| department_id | 党员人数 |
+---------------+----------+
|           102 |        2 |
|           103 |        1 |
+---------------+----------+
2 rows in set (0.00 sec)

14.统计各个部门的工资和平均工资并保留2为小数：

mysql> select department_id,round(avg(wages)),round(sum(wages)) from t_worker-> group by department_id;
+---------------+-------------------+-------------------+
| department_id | round(avg(wages)) | round(sum(wages)) |
+---------------+-------------------+-------------------+
|           101 |              6350 |             12700 |
|           102 |              8267 |             24800 |
|           103 |              5500 |              5500 |
+---------------+-------------------+-------------------+
3 rows in set (0.00 sec)

15.列出总人数大于等于3的部门号和总人数：

mysql> select department_id,count(department_id) from t_worker-> group by department_id-> having count(department_id) > 3;
Empty set (0.00 sec)