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SQL Joins Explained

The document discusses different types of SQL JOINs used to combine data from multiple tables. It describes INNER JOIN, which returns rows that match between tables; LEFT JOIN, which returns all rows from the left table and matched rows from the right table; RIGHT JOIN, which returns all rows from the right table and matched rows from the left table; and FULL JOIN, which returns all rows when there is a match in either table. Examples of SQL statements are provided for each JOIN type.

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115 views5 pages

SQL Joins Explained

The document discusses different types of SQL JOINs used to combine data from multiple tables. It describes INNER JOIN, which returns rows that match between tables; LEFT JOIN, which returns all rows from the left table and matched rows from the right table; RIGHT JOIN, which returns all rows from the right table and matched rows from the left table; and FULL JOIN, which returns all rows when there is a match in either table. Examples of SQL statements are provided for each JOIN type.

Uploaded by

Hassan Khan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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SQL JOIN

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

Different Types of SQL JOINs

Here are the different types of the JOINs in SQL:

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

       

SQL INNER JOIN Keyword

The INNER JOIN keyword selects records that have matching values in both
tables.
INNER JOIN Syntax
SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

SQL INNER JOIN Example

The following SQL statement selects all orders with customer information:

Example
SELECT Orders.OrderID, Customers.CustomerName
FROM Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

Note: The INNER JOIN keyword selects all rows from both tables as long as there
is a match between the columns. If there are records in the "Orders" table that do
not have matches in "Customers", these orders will not be shown.

SQL LEFT JOIN Keyword

The LEFT JOIN keyword returns all records from the left table (table1), and the
matched records from the right table (table2). The result is NULL from the right
side, if there is no match.

LEFT JOIN Syntax


SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;
Note: In some databases LEFT JOIN is called LEFT OUTER JOIN.

SQL LEFT JOIN Example

The following SQL statement will select all customers, and any orders they might
have:

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

The RIGHT JOIN keyword returns all records from the right table (table2), and the
matched records from the left table (table1). The result is NULL from the left side,
when there is no match.

RIGHT JOIN Syntax


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

Note: In some databases RIGHT JOIN is called RIGHT OUTER JOIN.


SQL RIGHT JOIN Example

The following SQL statement will return all employees, and any orders they might
have placed:

Example
SELECT Orders.OrderID, Employees.LastName, Employees.FirstName
FROM Orders
RIGHT JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID
ORDER BY Orders.OrderID;

SQL FULL OUTER JOIN Keyword


The FULL OUTER JOIN keyword returns all records when there is a match in left
(table1) or right (table2) table records.

Note: FULL OUTER JOIN can potentially return very large result-sets!

Tip: FULL OUTER JOIN and FULL JOIN are the same.

FULL OUTER JOIN Syntax


SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name = table2.column_name
WHERE condition;

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