MySQL case combat-MySQL database single table query two

Preface

This environment is based on Centos 7.8 system to build MySQL-5.7.14 for
specific construction, please refer to MySQL-5.7.14 environment construction

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Material preparation:

/* 素材 */
CREATE TABLE `emp`  (
  `empno` int(4) NOT NULL,
  `ename` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `job` varchar(255) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,
  `mgr` int(4) NULL DEFAULT NULL,
  `hiredate` date NOT NULL,
  `sai` int(255) NOT NULL,
  `comm` int(255) NULL DEFAULT NULL,
  `deptno` int(2) NOT NULL,
  PRIMARY KEY (`empno`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;

INSERT INTO `emp` VALUES (1001, '甘宁', '文员', 1013, '2000-12-17', 8000, NULL, 20);
INSERT INTO `emp` VALUES (1002, '黛绮丝', '销售员', 1006, '2001-02-20', 16000, 3000, 30);
INSERT INTO `emp` VALUES (1003, '殷天正', '销售员', 1006, '2001-02-22', 12500, 5000, 30);
INSERT INTO `emp` VALUES (1004, '刘备', '经理', 1009, '2001-04-02', 29750, NULL, 20);
INSERT INTO `emp` VALUES (1005, '谢逊', '销售员', 1006, '2001-09-28', 12500, 14000, 30);
INSERT INTO `emp` VALUES (1006, '关羽', '经理', 1009, '2001-05-01', 28500, NULL, 30);
INSERT INTO `emp` VALUES (1007, '张飞', '经理', 1009, '2001-09-01', 24500, NULL, 10);
INSERT INTO `emp` VALUES (1008, '诸葛亮', '分析师', 1004, '2007-04-19', 30000, NULL, 20);
INSERT INTO `emp` VALUES (1009, '曾阿牛', '董事长', NULL, '2001-11-17', 50000, NULL, 10);
INSERT INTO `emp` VALUES (1010, '韦一笑', '销售员', 1006, '2001-09-08', 15000, 0, 30);
INSERT INTO `emp` VALUES (1011, '周泰', '文员', 1006, '2007-05-23', 11000, NULL, 20);
INSERT INTO `emp` VALUES (1012, '程普', '文员', 1006, '2001-12-03', 9500, NULL, 30);
INSERT INTO `emp` VALUES (1013, '庞统', '分析师', 1004, '2001-12-03', 30000, NULL, 20);
INSERT INTO `emp` VALUES (1014, '黄盖', '文员', 1007, '2002-01-23', 13000, NULL, 10);
INSERT INTO `emp` VALUES (1015, '张三', '保洁员', 1001, '2013-05-01', 80000, 50000, 50);

Start query:

# 查看表结构
mysql> desc emp;
+----------+--------------+------+-----+---------+-------+
| Field    | Type         | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| empno    | int(4)       | NO   | PRI | NULL    |       |
| ename    | varchar(255) | YES  |     | NULL    |       |
| job      | varchar(255) | YES  |     | NULL    |       |
| mgr      | int(4)       | YES  |     | NULL    |       |
| hiredate | date         | NO   |     | NULL    |       |
| sai      | int(255)     | NO   |     | NULL    |       |
| comm     | int(255)     | YES  |     | NULL    |       |
| deptno   | int(2)       | NO   |     | NULL    |       |
+----------+--------------+------+-----+---------+-------+
8 rows in set (0.00 sec)

# 查看表信息
mysql> select * from emp;
+-------+-----------+-----------+------+------------+-------+-------+--------+
| empno | ename     | job       | mgr  | hiredate   | sai   | comm  | deptno |
+-------+-----------+-----------+------+------------+-------+-------+--------+
|  1001 | 甘宁      | 文员      | 1013 | 2000-12-17 |  8000 |  NULL |     20 |
|  1002 | 黛绮丝    | 销售员    | 1006 | 2001-02-20 | 16000 |  3000 |     30 |
|  1003 | 殷天正    | 销售员    | 1006 | 2001-02-22 | 12500 |  5000 |     30 |
|  1004 | 刘备      | 经理      | 1009 | 2001-04-02 | 29750 |  NULL |     20 |
|  1005 | 谢逊      | 销售员    | 1006 | 2001-09-28 | 12500 | 14000 |     30 |
|  1006 | 关羽      | 经理      | 1009 | 2001-05-01 | 28500 |  NULL |     30 |
|  1007 | 张飞      | 经理      | 1009 | 2001-09-01 | 24500 |  NULL |     10 |
|  1008 | 诸葛亮    | 分析师    | 1004 | 2007-04-19 | 30000 |  NULL |     20 |
|  1009 | 曾阿牛    | 董事长    | NULL | 2001-11-17 | 50000 |  NULL |     10 |
|  1010 | 韦一笑    | 销售员    | 1006 | 2001-09-08 | 15000 |     0 |     30 |
|  1011 | 周泰      | 文员      | 1006 | 2007-05-23 | 11000 |  NULL |     20 |
|  1012 | 程普      | 文员      | 1006 | 2001-12-03 |  9500 |  NULL |     30 |
|  1013 | 庞统      | 分析师    | 1004 | 2001-12-03 | 30000 |  NULL |     20 |
|  1014 | 黄盖      | 文员      | 1007 | 2002-01-23 | 13000 |  NULL |     10 |
|  1015 | 张三      | 保洁员    | 1001 | 2013-05-01 | 80000 | 50000 |     50 |
+-------+-----------+-----------+------+------------+-------+-------+--------+
15 rows in set (0.00 sec)


-- 1. 查询出部门编号为30的所有员工
	mysql> select ename from emp 
    -> where deptno=30;

-- 2. 所有销售员的姓名、编号和部门编号。
	mysql> select ename,empno,deptno 
    -> from emp
    -> where job='销售员';

-- 3. 找出奖金高于工资的员工。
	mysql> select ename from emp
    -> where comm>sai;

-- 4. 找出奖金高于工资60%的员工。
	mysql> select ename from emp
    -> where comm>sai*0.6;

-- 5. 找出部门编号为10中所有经理，和部门编号为20中所有销售员的详细资料。
	mysql> select * from emp
    -> where (deptno=10 and job='经理')
    -> or (deptno=20 and job='销售员');

-- 6. 找出部门编号为10中所有经理，部门编号为20中所有销售员，还有即不是经理又不是销售员但其工资大或等于20000的所有员工详细资料。
	mysql> select * from emp
    -> where (deptno=10 and job='经理')
    -> or (deptno=20 and job='销售员')
    -> or (job!='经理' and job!='销售员' or sai>=20000);
	
	mysql> select * from emp
    -> where (deptno=10 and job='经理')
    -> or (deptno=20 and job='销售员')
    -> or (job not in ('经理','销售员') or sai>=20000)
	
-- 7. 无奖金或奖金低于1000的员工。
	mysql> select ename from emp
    -> where comm is null or comm<1000;

-- 8. 查询名字由三个字组成的员工。
-- 注意：一个汉字占三个字节
	mysql> select * from emp
    -> where ename like '___';
	
	mysql> select * from emp
    -> where length(ename)=9;

-- 9.查询2000年入职的员工。
	mysql> select ename from emp
    -> where year(hiredate)=2000;

-- 10. 查询所有员工详细信息，用编号升序排序
	mysql> select * from emp
    -> order by empno;

-- 11. 查询所有员工详细信息，用工资降序排序，如果工资相同使用入职日期升序排序
	mysql> select * from emp
    -> order by sai desc,hiredate;

-- 12.查询每个部门的平均工资
	mysql> select job,group_concat(sai),avg(sai) from emp
    -> group by job;

-- 13.查询每个部门的雇员数量
	mysql> select deptno,count(1) from emp
    -> group by deptno;

-- 14.查询每种工作的最高工资、最低工资、人数
	mysql> select job,max(sai),min(sai),count(1) from emp
    -> group by job;