w3resource_MySQL练习：Basic_select_statement

w3resource_MySQL练习题：Basic_select_statement

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

Sample table: employees

-- 要点：as设置别名，as可省略
select first_name as "First Name", last_name as "Last Name"
from employees

　　

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

Sample table: employees

-- 要点：select时添加distinct获取唯一值
select distinct department_id
from employees

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

Sample table: employees

-- 要点：order by进行排序，desc进行降序排序
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)

Sample table: employees

-- 要点：select中可以进行数学运算
select first_name, last_name, salary, salary*0.15 as PF
from employees

　　

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

Sample table: employees

-- 要点：order by + asc
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

Sample table: employees

-- 要点：sum()加总
select sum(salary)
from employees

　　

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

Sample table: employees

-- 要点：max() + min()
select max(salary), min(salary)
from employees

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

Sample table: employees

-- 要点：avg()均值 + count()计数
select avg(salary), count(*)
from employees

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

Sample table: employees

-- 要点：count()
select count(*)
from employees

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

Sample table: employees

-- 要点：count() + distinct
select count(distinct job_id)
from employees

　　

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

Sample table: employees

-- 要点：upper()
select upper(first_name)
from employees

　　

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

Sample table: employees

-- 要点：left()从左开始取字符
select left(first_name, 3)
from employees

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

-- 要点：select可直接计算
select 171*214+625

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

Sample table: employees

-- 要点：concat()两列字符串组合
select concat(first_name, ' ', last_name)
from employees

　　

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

Sample table: employees

-- 要点：trim()去除两边空格
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

Sample table: employees

-- 要点：length()计算长度
select length(first_name)+first_name(last_name)
from employees

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

Sample table: employees

-- 要点：where里使用 REGEXP 实现正则效果
select *
from employees
where first_name REGEXP '[0-9]'

　　

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

Sample table: employees

-- 要点：limit限制取数量
select *
from employees
limit 10

　　

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

Note : Assume the salary field provides the 'annual salary' information.

Sample table: employees

-- 要点：round()实现小数位控制
select first_name, last_name, round(salary/12, 2) as 'Monthly Salary'
from employees