HR Data Base MySQL basic SELECT statement exercises.

출처는 https://www.w3resource.com/mysql-exercises/

 

1. Write a query to display the names (first_name, last_name) using alias name “First Name", "Last Name"

- select first_name "First Name", last_name "Last Name" from employees;

 

2. Write a query to get unique department ID from employee table.

- select distinct department_id from employees;

 

3. Write a query to get all employee details from the employee table order by first name, descending.

- select * from employees order by first_name desc;

 

4. Write a query to get the names (first_name, last_name), salary, PF of all the employees (PF is calculated as 15% of salary).

- select first_name, last_name, salary, salary * 0.15 "PF" from employees;

 

5. Write a query to get the employee ID, names (first_name, last_name), salary in ascending order of salary.

-select employee_id, first_name, last_name, salary from employees order by salary asc;

 

6. Write a query to get the total salaries payable to employees.

- select sum(salary) from employees;

 

7. Write a query to get the maximum and minimum salary from employees table.

- select max(salary), min(salary) from employees;

 

8. Write a query to get the average salary and number of employees in the employees table.

- select avg(salary), count(*) from employees;

 

9. Write a query to get the number of employees working with the company.

- select count(*) from employees;

 

10. Write a query to get the number of jobs available in the employees table. 

- select count(distinct job_id) from employees;

 

11. Write a query get all first name from employees table in upper case. 

- select upper(first_name) from employees;

 

12. Write a query to get the first 3 characters of first name from employees table. 

- select left(first_name, 3) from employees;

- select substring(first_name,1,3) from employees;

 

left()와 substring()의 차이?

 

13. Write a query to calculate 171*214+625. 

- select 171*214+625 "RESULT";

 

14. Write a query to get the names (for example Ellen Abel, Sundar Ande etc.) of all the employees from employees table.

- select concat(first_name, ' ', last_name) "Name" from employees;

 

15. Write a query to get first name from employees table after removing white spaces from both side.

- select trim(first_name) from employees;

 

16. Write a query to get the length of the employee names (first_name, last_name) from employees table. 

- select first_name, last_name, length(first_name)+length(last_name) "length" from employees;

 

17. Write a query to check if the first_name fields of the employees table contains numbers. 

- select * from employees where first_name regexp '[0-9]';

 

18. Write a query to select first 10 records from a table. 

- select * from employees limit 10;

 

19. Write a query to get monthly salary (round 2 decimal places) of each and every employee.

- select first_name, last_name, round(salary/12, 2) as "Monthly Salary" from employees;