数据库数据插入与查询
要求：
准备工作：
（一）新建数据库
mysql> create database mydb8_worker;
Query OK, 1 row affected (0.00 sec)mysql> use mydb8_worker;
Database changed
（二）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');
（三）插入数据
mysql> insert into t_worker values (101,1001,'2015-5-4',7500,'群众','张春燕','1990-7-1');
Query OK, 1 row affected (0.02 sec)mysql> insert into t_worker values (101,1002,'2019-2-6',5200,'团员','李名博','1997-2-8');
Query OK, 1 row affected (0.01 sec)mysql> insert into t_worker values (102,1003,'2008-1-4',10500,'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,'群众','赵小军','1994-9-5');
Query OK, 1 row affected (0.02 sec)mysql> insert into t_worker values (102,1005,'2014-4-1',8800,'党员','钱有财','1992-12-30');
Query OK, 1 row affected (0.01 sec)mysql> insert into t_worker values (103,1006,'2019-5-5',5500,'党员','孙菲菲','1996-9-2');
Query OK, 1 row affected (0.01 sec)
完成查询：
（1）显示所有职工的基本信息；
mysql> select * from t_worker;
（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;
（3）求出所有职工的人数；提示：找主键
mysql> select count(worker_id) from t_worker;
（4）列出最高工资和最低工资；
mysql> select max(wages),min(wages) from t_worker;
（5）列出职工的平均工资和总工资；
mysql> select avg(wages),sum(wages) from t_worker;
（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 workerdate comment '工作日期表' as select worker_id,worker_ddate,name from t_worker;
Query OK, 6 rows affected (0.03 sec)
Records: 6 Duplicates: 0 Warnings: 0mysql> select * from workerdate;
（7）列出所有党员的年龄；
mysql> select (year(now())-year(borth_date)) '年龄' from t_worker where politics='党员';
（8）列出工资在4000~8000的所有职工姓名；
mysql> select name,wages from t_worker where wages>4000 and wages<8000;
（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%';
（10）列出所有部门号为102和103且不是党员的职工号、姓名。
第一种：
mysql> select worker_id,name from t_worker where (department_id=102 or department_id=103) and politics !='党员';
第二种：
mysql> select worker_id,name from t_worker where department_id in (102,103) and politics !='党员';
（11）将职工表t_worker中的职工按出生的先后顺序排序；
mysql> select name,borth_date from t_worker order by borth_date;（顺序排列）
mysql> select name,borth_date from t_worker order by borth_date desc;（倒序排列）
（12）显示工资最高的前三名职工的职工号和姓名；
mysql> select worker_id,name from t_worker order by wages desc limit 3;
（13）求出各部门党员的人数；
mysql> select count(politics),department_id from t_worker where politics='党员' group by department_id;
（14）统计各部门的工资和平均工资，并保留两位小数；
mysql> select sum(wages),round(avg(wages),2),department_id from t_worker group by department_id;
（15）列出总人数大于等于3的部门号和总人数；
mysql> select department_id,count(worker_id) from t_worker group by department_id having count(worker_id)>=3;
