I learned database at station B (V): DQL exercise

Last one ： I am here b Station learning database （ Four ）：DQL

DQL Basic query operation exercise

Exercise one ：
Data preparation ：

1、 Query all student information in the table

select * 
from student;

2、 Look up the names of all the students and their English scores

select name,english 
from student;

3、 Filter out duplicate data

selcet distct * 
from student;

4、 Count the total score of each student

select name,(chinese + english + math) as total_score 
from student;

5、 Add... To the total score of all students 10 Points of specialty points of

select name,(chinese + english + math +10) as total_score 
from student;

6、 Use aliases to indicate student scores

select name,chinese' Chinese achievement ',english' English scores ',math' Math scores ' 
from student;

7、 Query English score greater than 90 Classmate

select * 
from student 
where english > 90;

8、 Total query score greater than 200 All my classmates

select * 
from student
where (chinese + english + math)> 200;

9、 Query English scores in 80-90 Between the students

select * 
from student
where english between 80 and 90;
 perhaps 
select * 
from student
where english >= 80 and <= 90;

10、 Query English score is not in 80-90 Between the students

 The first one is 
select * 
from student
where not (english between 80 and 90);
 The second kind 
select * 
from student
where english not between 80 and 90;
 The third kind of 
select * 
from student
where not (english >= 80 and <=90);
 A fourth 
select * 
from student
where english < 80 || english > 90;

11、 Query math score is 89,90,91 Classmate

select * 
from student
where math in(89,90,91);

12、 Check the English scores of all students surnamed Li

select name,english
from student
where name like ' Li %';

13、 Query math score 80 And Chinese is divided into 80 Classmate

select * 
from student
where math = 80 and chinese = 80;

14、 Query English 80 Or total score 200 Classmate

select * 
from student
where english = 80 and (chinese + english + math) = 200;

15、 Output the math scores in descending order

select *
from stdent 
order by math desc;

16、 After sorting the total score, output , And then output it from high to low

select *
from stdent 
order by (chinese + english + math) desc;

17、 Sort the students' grades by their surname Li

select *
from student 
where name like ' Li %' 
order by (chinese + english + math) desc;

18、 How many boys and girls are there , And output the number of people in descending order , The number of people queried is greater than 4 Number of men and women

select gender,count(*) as toatl-cnt
from student 
group by gender
having total_cnt > 4
order by total_cnt desc

Exercise 2
Data preparation ：


1、 By employee The number is not in ascending order 10 Employee information of department No

select * 
from emp
where deptno != 10
order by empno desc; 

2、 The second letter of the query name is not ’A’ And the salary is greater than 1000 Employee information for , In descending order of annual salary

select *
from emp
where ename not like '_A%' and sal >1000
order by (12 * sal + innull(comm,0))
#ifnull(comm,0)  If comm The value of is null, As if 0, Not for null, Then it is still the original value 

3、 Average salary for each department

 The first one is 
select deptno,avg(sal)
from emp
group by deptno;
 The second kind 
select deptno,avg(sal) as avg_sal 
from emp
group by deptno
order by avg_sal desc;

4、 Ask for the highest salary in each department

select deptno,max(sal) max_avg 
from emp 
group by deptno;

5、 Ask for the highest salary for each position in each department

select deptno,job,max(sal)
from emp
group by deptno,job
order by deptno;

6、 The average salary is greater than 2000 Department number of

select deptno,avg(sal) avg_sal
from emp
group by deptno
having avg_sal >2000;

7、 The average salary of the Department will be greater than 1500 The department number of the , Rank by department average salary in descending order

select deptno,avg(sal) avg_sal
from emp
group by deptno
having avg_sal >1500
order by avg_sal desc;

8、 Choose the name of the employee in the company who has the bonus , Wages

select *
from emp
where comm is not null;

9、 Find out the difference between the maximum wage and the minimum wage

select max(sal) - min(sal) ' Pay gap '
from emp;