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The SQL JOIN Clause

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

Here are the different types of JOINs in SQL:

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

Look at an order in "Orders" table:

OrderID CustomerID OrderDate
10308 2 1996-09-18

Then, look at a customer in the "Customers" table:

CustomerID CustomerName ContactName Country
2 Ana Trujillo Emparedados y helados Ana Trujillo Mexico

Here we see 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:

Example

SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDateFROM OrdersINNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID; Try it Yourself »

and it will produce something like this:

OrderID CustomerName OrderDate
10308 Ana Trujillo Emparedados y helados 1996-09-18
10365 Antonio Moreno Taquería 1996-11-27
10383 Around the Horn 1996-11-15
10355 Around the Horn 1996-12-16
10278 Berglunds snabbköp 1996-12-16
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