数据库查询

前置条件

1.建库建表

mysql> create database  mydb8_worker;
Query OK, 1 row affected (0.01 sec)

mysql> use mydb8_worker;
Database changed

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 (0.02 sec)

2.插入数据

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 (0.01 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 (0.01 sec)

mysql>  insert into t_worker values (102,1005,'2014-4-1',8800.00,'党员','钱有财','1992-12-30');
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 (0.01 sec)

mysql> 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','李名博','1997-2-8');
Query OK, 1 row affected (0.01 sec)

查询

（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     | 李名博    | 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    | 1992-12-30 |
|           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(worker_id) from t_worker;
+------------------+
| count(worker_id) |
+------------------+
|                6 |
+------------------+
1 row in set (0.01 sec)

（4）列出最高工资和最低工资

mysql> select max(wages) as '最高工资', min(wages) as '最低工资' from t_worker;
+--------------+--------------+
| 最高工资     | 最低工资     |
+--------------+--------------+
|     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 avg(wages) as '平均工资', sum(wages) as '总工资' from t_worker;
+--------------+-----------+
| 平均工资     | 总工资    |
+--------------+-----------+
|  7166.666667 |  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 t_workdate select worker_id ,name from t_worker;
Query OK, 6 rows affected (0.02 sec)
Records: 6  Duplicates: 0  Warnings: 0

mysql> select * from t_workdate;
+-----------+-----------+
| worker_id | name      |
+-----------+-----------+
|      1001 | 张春燕    |
|      1002 | 李名博    |
|      1003 | 王博涵    |
|      1004 | 赵小军    |
|      1005 | 钱有财    |
|      1006 | 孙菲菲    |
+-----------+-----------+
6 rows in set (0.00 sec)

（7）显示所有党员的年龄

mysql> select name '姓名',year(now())-year(borth_date) '年龄' from t_worker where politics = '党员';
+-----------+--------+
| 姓名      | 年龄   |
+-----------+--------+
| 王博涵    |     41 |
| 钱有财    |     32 |
| 孙菲菲    |     28 |
+-----------+--------+
3 rows in set (0.00 sec)

(8)、列出工资在4000-8000之间的所有职工姓名

mysql> select name from t_worker where wages between 4000 and 8000;
+-----------+
| name      |
+-----------+
| 张春燕    |
| 李名博    |
| 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      |
+-----------+
| 李名博    |
| 孙菲菲    |
+-----------+
2 rows in set (0.00 sec)

(10)列出所有部门号为102和103日不是党员的职工号、姓名

mysql> select worker_id '职工号',name '姓名' from t_worker where department_id in(102,103) and politics != '党员';
+-----------+-----------+
| 职工号    | 姓名      |
+-----------+-----------+
|      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    | 1992-12-30 |
|           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     | 李名博    | 1997-02-08 |
+---------------+-----------+-------------+----------+----------+-----------+------------+
6 rows in set (0.00 sec)

(12)显示工资最高的前3名职工的职工号和姓名

mysql> select worker_id '职工号',name '姓名' from t_worker order by wages desc limit 3;
+-----------+-----------+
| 职工号    | 姓名      |
+-----------+-----------+
|      1003 | 王博涵    |
|      1005 | 钱有财    |
|      1001 | 张春燕    |
+-----------+-----------+
3 rows in set (0.00 sec)

(13)求出各部门党员的人数

mysql> select department_id as '部门编号', sum(case when politics = '党员' then 1 else 0 end) as '党员人数' from t_worker group by department_id;
+--------------+--------------+
| 部门编号     | 党员人数     |
+--------------+--------------+
|          101 |            0 |
|          102 |            2 |
|          103 |            1 |
+--------------+--------------+
3 rows in set (0.00 sec)

(14)统计各部门的工资和平均工资并保留2位小数

mysql> select department_id '部门编号',round(sum(wages),2) '总工资' ,round(avg(wages),2) '平均工资' from t_worker  group by department_id;
+--------------+-----------+--------------+
| 部门编号     | 总工资    | 平均工资     |
+--------------+-----------+--------------+
|          101 |     12700 |         6350 |
|          102 |     24800 |      8266.67 |
|          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 '部门编号', count(worker_id) from t_worker  group by department_id having count(worker_id)>=3;
+--------------+------------------+
| 部门编号     | count(worker_id) |
+--------------+------------------+
|          102 |                3 |
+--------------+------------------+
1 row in set (0.00 sec)