SQL学习记录（三）-DQL语句

#DQL
CREATE TABLE emp(
id INT COMMENT'编号',
workno VARCHAR(10) COMMENT'工号',
NAME VARCHAR(10) COMMENT'姓名',
gender CHAR COMMENT'性别',
age TINYINT UNSIGNED COMMENT'年龄',
idcard CHAR(18) COMMENT'身份证号',
workaddress VARCHAR(50) COMMENT'工作编号',
entrydate DATE COMMENT'入职时间'
)COMMENT '员工表';

#插入数据
insert into emp (id, workno, name, gender, age, idcard,workaddress, entrydate)
VALUES 
(1,'1','柳岩','女',20,'123456789012345678','北京','2000-01-01'),
(2,'2','张无忌','男',18,'123456789012345670','北京','2005-09-01'),
(3,'3','韦一笑','男',38,'123456789712345670','上海','2005-08-01'),
(4,'4','赵敏','女',18,'123456757123845670','北京','2009-12-01'),
(5,'5','小昭','女',16,'123456769012345678','上海','2007-07-01'),
(6,'6','杨道','男',28,'12345678931234567X','北京','2006-01-01'),
(7,'7','范瑶','男',40,'123456789212345670','北京','2005-05-01'),
(8,'8','黛绮丝','女',38,'123456157123645670','天津','2015-05-01'),
(9,'9', '范凉凉','女',45,'123156789012345678','北京','2010-04-01'),
(10,'10','陈友谅','男',53,'123456789012345670','上海','2011-01-01'),
(11,'11','张士诚','男',55,'123567897123465670','江苏','2015-05-01'),
(12,'12','常遇春','男',32,'123446757152345670','北京','2004-02-01'),
(13,'13','张三丰','男',88,'123656789012345678','江苏','2020-11-01'),
(14,'14','灭绝','女',65,'123456719012345670','西安','2019-05-01'),
(15,'15','胡青牛','男',70,'12345674971234567X','西安','2018-04-01'),
(16,'16','周芷若','女',18,null,'北京','2012-06-01');

#查询指定字段ame,workno,age
SELECT name,workno,age FROM emp;
#查询所有字段返回
SELECT id,workno,`name`,gender,age,idcard,workaddress,entrydate FROM emp;

SELECT * FROM emp;

#查询工作地址
SELECT workaddress as '工作地址' FROM emp;
SELECT workaddress '工作地址' FROM emp;
#查询工作地址（不重复）DISTINCT
SELECT DISTINCT workaddress '工作地址' FROM emp;

--1.查询年龄等于 88 的员工
SELECT * FROM emp WHERE age = 88;
--2.查询年龄小于 20的员工信息
SELECT * FROM emp WHERE age <20;
--3.查询年龄小于等于 20 的员工信息
SELECT * FROM emp WHERE age <=20;
--4.查询没有身份证好的员工信息
SELECT * FROM emp WHERE idcard is NULL;
--5.查询有身份证号的员工信息
SELECT * FROM emp WHERE idcard is NOT NULL;
--6.查询年龄不等于 88 的员工信息
SELECT * FROM emp WHERE age !=88;
SELECT * FROM emp WHERE age <>88;
--7.查询年龄在15岁(包含)到20岁(包含)之间的员工信息
SELECT * FROM emp WHERE age >= 15 && age <=20;
SELECT * FROM emp WHERE age >= 15 AND age <=20;

SELECT * FROM emp WHERE age BETWEEN 15 AND 20;
--8.查询性别为女且年龄小于 25岁的员工信息
SELECT * FROM emp WHERE gender = '女' AND age <25;

--9.查询年龄等于18或20或40的员工信息
SELECT * FROM emp WHERE age = 18 or age = 20 or age =40;
SELECT * FROM emp WHERE age IN(18,20,40);

--10.查询姓名为两个字的员工信息_%
SELECT * FROM emp WHERE NAME LIKE '__';
--11、查询身份证最后一位是X的员工信息
SELECT * FROM emp WHERE idcard LIKE '%X';

--聚合函数
--1.统计该企业员工数量
SELECT count(*) FROM emp;
SELECT COUNT(idcard) FROM emp;

--2.统计该企业员工的平均年龄
SELECT avg(age) FROM emp; 

--3.统计该企业员工的最大年龄
SELECT max(age) FROM emp;

--4.统计该企业员工的最小年龄
SELECT min(age) FROM emp;

--5、统计西安地区员工年龄之和
SELECT sum(age) FROM emp WHERE workaddress = '西安';

--分组查询
--1.根据性别分组统计男性员工和女性员工的数量
SELECT gender,count(*) FROM emp GROUP BY gender ;
--2.根据性别分组，统计男性员工和女性员工的平均年龄
SELECT gender,avg(age) FROM emp GROUP BY gender ;

--3.查询年龄小于45的员工 ，并根据工作地址分组 ，获取员工数量大于等于3的工作地址
SELECT workaddress,count(*) address_count FROM emp WHERE age < 45 GROUP BY workaddress HAVING address_count>=3;

--排序查询
--1.根据年龄对公司的员工进行升序排序
SELECT * FROM emp ORDER BY age asc;#升序
SELECT * FROM emp ORDER BY age desc;#倒序

SELECT * FROM emp ORDER BY age;
--2.根据入职时间，对员工进行降序排序
SELECT * FROM emp ORDER BY entrydate desc;
--3.根据年龄对公司的员工进行升序排序，年龄相同，再按照入职时间进行降序排序
SELECT * FROM emp ORDER BY age asc , entrydate desc;
SELECT * FROM emp ORDER BY age asc , entrydate ASC;

--1.查询年龄为20,21,22,23岁的女性员工信息。
SELECT *FROM emp WHERE gender = '女' and age in(20,211,22,23);

--2.查询性别为男，并且年龄在 20-40 岁(含)以内的姓名为三个字的员工。
SELECT * FROM emp WHERE gender = '男' and ( age BETWEEN 20 and 40 ) and NAME LIKE '___';

--3.统计员工表中，年龄小于60岁的，男性员工和女性员工的人数。
SELECT gender,count(*) FROM emp where age<60 GROUP BY gender; 

--4，查询所有年龄小于等于35岁员工的姓名和年龄，并对査询结果按年龄升序排序，如果年龄相同按入职时间降序排序。
SELECT name , age FROM emp WHERE age<=35 ORDER BY age asc , entrydate DESC;

--5.查询性别为男，且年龄在20-40 岁(含)以内的前5个员工信息，对査询的结果按年龄升序排序，年龄相同按入职时间升序排序
SELECT * FROM emp WHERE gender = '男' and age BETWEEN 20 and 40 ORDER BY age asc , entrydate asc LIMIT 5 ;

--查询年龄大于15的员工的姓名、年龄,并根据年龄进行升序排序
SELECT e.NAME ename,e.age eage FROM emp e WHERE e.age >15 ORDER BY age asc;

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