INNER JOIN

What is INNER JOIN?

An INNER JOIN is a type of SQL join that returns only the rows that have matching values in both tables. It is used to combine data from two or more tables based on a related column.

Syntax of INNER JOIN

SELECT columns
FROM table1
INNER JOIN table2
ON table1.column = table2.column;

• table1, table2 – Names of the tables you want to join.
• column – The common column used to match records in both tables.
• columns – The list of columns you want to display in the result.

How INNER JOIN Works

1. SQL looks for matching values in the specified columns of both tables.
2. Only rows that satisfy the matching condition are returned.
3. Rows with no match in either table are excluded.

Example 1: Basic INNER JOIN

Suppose we have two tables:

Customers
CustomerID, Name

Orders
OrderID, CustomerID, OrderDate

We want a list of customers with their orders:

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

Result:
Only customers who have placed an order will appear in the result. Customers without orders are excluded.

Example 2: INNER JOIN with Multiple Columns

You can join on more than one column if necessary:

SELECT A.Name, B.OrderID
FROM Customers A
INNER JOIN Orders B
ON A.CustomerID = B.CustomerID AND A.Region = B.Region;

This will return rows where both CustomerID and Region match in both tables.

Key Points to Remember

• INNER JOIN only returns matching rows.
• If no match exists, the row is not included.
• Multiple INNER JOINs can be used to join more than two tables.
• Aliases (like A and B) can simplify queries with long table names.