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A JOIN clause is used to combine rows from two or more tables, based on a related column between them
A JOIN
clause is used to combine rows from two or more tables, based on
a related column between them.
Let's look at a selection from the "Orders" table:
OrderID | CustomerID | OrderDate |
---|---|---|
10308 | 2 | 1996-09-18 |
10309 | 37 | 1996-09-19 |
10310 | 77 | 1996-09-20 |
Then, look at a selection from the "Customers" table:
CustomerID | CustomerName | ContactName | Country |
---|---|---|---|
1 | Alfreds Futterkiste | Maria Anders | Germany |
2 | Ana Trujillo Emparedados y helados | Ana Trujillo | Mexico |
3 | Antonio Moreno Taquería | Antonio Moreno | Mexico |
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:
SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate
FROM Orders
INNER JOIN Customers ON Orders.CustomerID=Customers.CustomerID;
and it will produce something like this:
OrderID | CustomerName | OrderDate |
---|---|---|
10308 | Ana Trujillo Emparedados y helados | 9/18/1996 |
10365 | Antonio Moreno Taquería | 11/27/1996 |
10383 | Around the Horn | 12/16/1996 |
10355 | Around the Horn | 11/15/1996 |
10278 | Berglunds snabbköp | 8/12/1996 |
INNER JOIN
: Returns records that have matching values in both tablesLEFT JOIN
: Returns all records from the left table, and the matched records from the right tableRIGHT JOIN
: Returns all records from the right table, and the matched records from the left tableCROSS JOIN
: Returns all records from both
tablesInsert the missing parts in the JOIN
clause to join the two tables Orders
and Customers
,
using the CustomerID
field in both tables as the relationship between the two tables.
SELECT * FROM Orders LEFT JOIN Customers =
;