what is left join in sql

1 year ago 157

In SQL, the LEFT JOIN clause is used to combine two tables based on a specified condition. The main features of a LEFT JOIN are:

It returns all records from the left table and the matching records from the right table

If there is no match between the tables, the result is NULL from the right side

The left table is mandatory, and the right table is optional

The syntax for a LEFT JOIN is as follows:

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

For example, consider two tables, Customers and Orders. A LEFT JOIN can be used to select all customers and any orders they might have, even if there are no matches in the Orders table:

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
LEFT JOIN Orders
ON Customers.CustomerID = Orders.CustomerID
ORDER BY Customers.CustomerName;

In this query, the LEFT JOIN returns all records from the Customers table, even if there are no matches in the Orders table