Introduction to querying mysql database forms and using functions

The following mainly brings you query mysql database forms and use functions, I hope these contents can bring you practical use, which is also the main purpose of my editing query mysql database forms and use functions this article. Okay, no more nonsense, let's go straight to the following.

Single table query

Prepare an employee list company.employee

Employee number emp_id int

Employee name emp_name varchar(30)

Employee sex enum

hire date hire_date

post varchar(50)

Job description job_description varchar(50)

salary double(15,2)

Office int

dep_id int

A simple query of the table

Select * from employee; //View all

Select Field 1, Field 2,... field n from table name

Avoid repeating the keyword distinct

Select distinct post from employee

Relational operators: + - *, %

Select emp_name salary*12 from employee;

As alias

Select emp_name as name salary*12 as salary from employee;

define display format concat() function for concatenating strings

Select concat (emp_name,'annual salary', salary*12) as Employee Annual Salary

From employee;

II. Query by condition

conditional query conditional expression

Comparison operator: > = 100000;

Keyword query between and

Select emp_name from employee

Where salary between 5000 and 15000; //Salary between 5000 and 15000

Select emp_name from employee

Where salary is not between 5000 and 15000; //Person whose salary is not between 5000 and 15000

Keyword query is null

Select emp_name,job_description from employee

Where job_description is null; //View employees whose job description is null

Select emp_name,job_description from employee

Where job_description is not null; //View non-null employee job description

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