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SQL Joins

Ajeet Singh
05/04/2017 0 0

SQL Joins

SQL joins are used to combine rows from two or more tables.

SQL JOIN

An SQL JOIN clause is used to combine rows from two or more tables, based on a common field between them.

The most common type of join is SQL INNER JOIN (simple join). An SQL INNER JOIN returns all rows from multiple tables where the join condition is met.

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, have a 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, if we run the following SQL statement (that contains an INNER JOIN):

Example

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

Try it Yourself »

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

Different SQL JOINs

Before we continue with examples, we will list the types of the different SQL JOINs you can use:

  • INNER JOIN: Returns all rows when there is at least one match in BOTH tables
  • LEFT JOIN: Return all rows from the left table, and the matched rows from the right table
  • RIGHT JOIN: Return all rows from the right table, and the matched rows from the left table
  • FULL JOIN: Return all rows when there is a match in ONE of the tables

SQL INNER JOIN Keyword

SQL INNER JOIN Keyword

The INNER JOIN keyword selects all rows from both tables as long as there is a match between the columns in both tables.

SQL INNER JOIN Syntax

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

or:

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

PS! INNER JOIN is the same as JOIN.

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table:

CustomerID

CustomerName

ContactName

Address

City

PostalCode

Country

1

Alfreds Futterkiste

Maria Anders

Obere Str. 57

Berlin

12209

Germany

2

Ana Trujillo Emparedados y helados

Ana Trujillo

Avda. de la Constitución 2222

México D.F.

05021

Mexico

3

Antonio Moreno Taquería

Antonio Moreno

Mataderos 2312

México D.F.

05023

Mexico

And a selection from the "Orders" table:

OrderID

CustomerID

EmployeeID

OrderDate

ShipperID

10308

2

7

1996-09-18

3

10309

37

3

1996-09-19

1

10310

77

8

1996-09-20

2

SQL INNER JOIN Example

The following SQL statement will return all customers with orders:

Example

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

Try it Yourself »

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

 

SQL LEFT JOIN Keyword

SQL LEFT JOIN Keyword

The LEFT JOIN keyword returns all rows from the left table (table1), with the matching rows in the right table (table2). The result is NULL in the right side when there is no match.

SQL LEFT JOIN Syntax

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

or:

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

PS! In some databases LEFT JOIN is called LEFT OUTER JOIN.

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table:

CustomerID

CustomerName

ContactName

Address

City

PostalCode

Country

1

Alfreds Futterkiste

Maria Anders

Obere Str. 57

Berlin

12209

Germany

2

Ana Trujillo Emparedados y helados

Ana Trujillo

Avda. de la Constitución 2222

México D.F.

05021

Mexico

3

Antonio Moreno Taquería

Antonio Moreno

Mataderos 2312

México D.F.

05023

Mexico

And a selection from the "Orders" table:

OrderID

CustomerID

EmployeeID

OrderDate

ShipperID

10308

2

7

1996-09-18

3

10309

37

3

1996-09-19

1

10310

77

8

1996-09-20

2

SQL LEFT JOIN Example

The following SQL statement will return 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;

Try it Yourself »

Note: The LEFT JOIN keyword returns all the rows from the left table (Customers), even if there are no matches in the right table (Orders).

 

SQL RIGHT JOIN Keyword

SQL RIGHT JOIN Keyword

The RIGHT JOIN keyword returns all rows from the right table (table2), with the matching rows in the left table (table1). The result is NULL in the left side when there is no match.

SQL RIGHT JOIN Syntax

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

or:

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

PS! In some databases RIGHT JOIN is called RIGHT OUTER JOIN.

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Orders" table:

OrderID

CustomerID

EmployeeID

OrderDate

ShipperID

10308

2

7

1996-09-18

3

10309

37

3

1996-09-19

1

10310

77

8

1996-09-20

2

And a selection from the "Employees" table:

EmployeeID

LastName

FirstName

BirthDate

Photo

Notes

1

Davolio

Nancy

12/8/1968

EmpID1.pic

Education includes a BA in psychology.....

2

Fuller

Andrew

2/19/1952

EmpID2.pic

Andrew received his BTS commercial and....

3

Leverling

Janet

8/30/1963

EmpID3.pic

Janet has a BS degree in chemistry....

SQL RIGHT JOIN Example

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

Example

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


Try it Yourself »

Note: The RIGHT JOIN keyword returns all the rows from the right table (Employees), even if there are no matches in the left table (Orders).

SQL FULL OUTER JOIN Keyword

â?® Previous

SQL FULL OUTER JOIN Keyword

The FULL OUTER JOIN keyword returns all rows from the left table (table1) and from the right table (table2).

The FULL OUTER JOIN keyword combines the result of both LEFT and RIGHT joins.

SQL FULL OUTER JOIN Syntax

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

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the "Customers" table:

CustomerID

CustomerName

ContactName

Address

City

PostalCode

Country

1

Alfreds Futterkiste

Maria Anders

Obere Str. 57

Berlin

12209

Germany

2

Ana Trujillo Emparedados y helados

Ana Trujillo

Avda. de la Constitución 2222

México D.F.

05021

Mexico

3

Antonio Moreno Taquería

Antonio Moreno

Mataderos 2312

México D.F.

05023<

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