LEFT and RIGHT JOIN

LEFT JOIN returns all rows from the left table, plus matching rows from the right. Where there is no match, the right columns are NULL.

sql

### SELECT Customers.CustomerName, Orders.OrderID

### FROM Customers

### LEFT JOIN Orders

### ON Customers.CustomerID = Orders.CustomerID;

"Around the Horn" has no order, so OrderID is NULL - but the customer still appears.

RIGHT JOIN

RIGHT JOIN is the mirror: all rows from the right table, plus matching left rows.

sql

### SELECT Customers.CustomerName, Orders.OrderID

### FROM Orders

### RIGHT JOIN Customers

### ON Orders.CustomerID = Customers.CustomerID;

Which side is which?

• The table written first (after FROM) is the left table.
• The table after JOIN is the right table.
• LEFT JOIN keeps all of the left; RIGHT JOIN keeps all of the right.

TL;DR

• LEFT JOIN keeps every left row; missing right values become NULL.
• RIGHT JOIN keeps every right row; missing left values become NULL.
• The order of the tables decides left and right.