SQL Joins

A SQL JOIN clause is used to combine rows from two or more tables, based on a related column between them,

Example:

SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
FROM Orders
INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;

Notice that the “CustomerID” column in the “Orders” table refers to the “CustomerID” in the “Customers” table. The relationship between the two tables above is the “CustomerID” column.

Then, we can create the following SQL statement (that contains an INNER JOIN), that selects records that have matching values in both tables:

Different Types of SQL JOINS:

Here are the different types of the JOINs in SQL:

• (INNER) JOIN: Returns records that have matching values in both tables
• LEFT (OUTER) JOIN: Return all records from the left table, and the matched records from the right table
• RIGHT (OUTER) JOIN: Return all records from the right table, and the matched records from the left table
• FULL (OUTER) JOIN: Return all records when there is a match in either left or right table

1 : INNER JOIN Syntax
SELECT column_name(s) FROM table1 INNER JOIN table2 ON table1.column_name = table2.column_name;

2 : LEFT JOIN Syntax
SELECT column_name(s)
FROM table1
LEFT JOIN table2 ON table1.column_name = table2.column_name;

3 :RIGHT JOIN Syntax
SELECT column_name(s) FROM table1 RIGHT JOIN table2 ON table1.column_name = table2.column_name;

4 : FULL OUTER JOIN Syntax
SELECT column_name(s) FROM table1 FULL OUTER JOIN table2 ON table1.column_name = table2.column_name;