SQL Join query is used to join the two tables i.e add or combine two or more tables .
This clause take data from two or more table in database and then combine them to produce new table . Joining is based upon the common fields from the tables .
Advantage :
Using this you can access more than one table with the help of select statement .
Join has 4 types :
*1) Inner Join : * it also known as simple join , it is widely used .

Example :

First Table name : Employee_Info

 
Employee_Id    Employee_name            Employee_Age          Employee _Salary
  1            Mukesh                  23                           100000
  2            Ayush                   24                           200000
  3            Ishan                   20                           400000
  4            Pranav                  35                           700000
  5            Abhishek                26                           800000
  6            Ravi                    25                           300000
  7            David                   40                           800000

Second Table name : student

    Student_Id  Student_name            Student_Age          Student_Id
       1        Mukesh                  23                    1
       3        Ayush                   24                    2
       4        Ishan                   20                    4
       16        Pranav                  35                    7
       15        Abhishek                26                    8
       12        Ravi                    25                    3

Now to join these above two tables then you can use simple join see below :

select Employee_Id , Employee_name , Student_name from Employee_Info e , student s where e.Employee_Id = s.Student_Id ;

Output : Onlye common column will come

Employee _Id       Employee_name                 Student_name 
        1            Mukesh                          Mukesh
        3            Ishan                           Ayush
        4            Pranav                          Ishan