SQL - JOIN

The SQL JOIN clause is used to combine rows of two or more tables based on common column between them. There are four types of JOINs in the SQL:

• INNER JOIN: Returns records based on matching rows in both tables.
• LEFT JOIN: Returns records which contains all rows from left table and matching rows from right tables.
• RIGHT JOIN: Returns records which contains all rows from right table and matching rows from left tables.
• FULL JOIN: Returns records which contains all rows from both tables.

Example:

Consider a database tables called Employee and Contact_Info with the following records:

Table 1: Employee table

Table 2: Contact_Info table

• The INNER JOIN clause is used with Employee and Contact_Info tables based on common column EmpID. It returns Name, Age and Address columns based on match in both tables. The SQL code is given below:

  SELECT Employee.Name, Employee.Age, Contact_Info.Address 
  FROM Employee
  INNER JOIN Contact_Info
  ON Employee.EmpID = Contact_Info.EmpID
  

  
  

  This will produce the result as shown below:

  Name	Age	Address
  Marry	24	XXX, Brooklyn, New York, USA
  Jo	27	XXX, Grenelle, Paris, France
  Kim	30	XXX, Geuzenveld, Amsterdam, Netherlands
  Huang	28	XXX, Yizhuangzhen, Beijing, China