SQL Outer Join Example

This article explains SQL OUTER JOIN syntax and gives an example on how to use OUTER JOIN

Outer join joined table will contain all records from both the tables (A and B) and fill in NULL for missing matches on either side.

OUTER JOIN and FULL JOIN are the same in terms of terminology.

You can use following links to view the different types of SQL JOINs :

  1. Inner Join
  2. Left Join
  3. Right Join
  4. Outer Join

Outer Join Visual Representation

SQL outer join

SQL outer join




Outer Join Syntax

This query will return the joined result of all records in both tables

SELECT Table_A.column1, Table_B.column2...
FROM Table_A A
FULL JOIN Table_B B
ON A.Key = B.Key

Outer Join Example

We will create 3 tables

  1. CUSTOMER
  2. PRODUCT
  3. ORDER

A customer can order products. In the ORDER table we hold the customer ID and the quantity of each product the customer has ordered.

Database diagram showing customer, product and order relationship

Database diagram showing customer, product and order relationship

Use following SQL scripts to create the three tables.

Create CUSTOMER table

CREATE TABLE `CUSTOMER` (
  `id` INT NOT NULL,
  `name` VARCHAR(45) NOT NULL,
  PRIMARY KEY (`id`));

Create PRODUCT table

CREATE TABLE `PRODUCT` (
  `id` INT NOT NULL,
  `name` VARCHAR(45) NOT NULL,
  `price` DECIMAL(7,2) NOT NULL,
  PRIMARY KEY (`id`));

Create ORDER table

CREATE TABLE `ORDER` (
  `id` INT NOT NULL,
  `date` DATETIME NOT NULL,
  `customer_id` INT NOT NULL,
  `product_id` INT NOT NULL,
  `quantity` INT NOT NULL,
  PRIMARY KEY (`id`),
  INDEX `product_id_idx` (`product_id` ASC) VISIBLE,
  INDEX `customer_id_idx` (`customer_id` ASC) VISIBLE,
  CONSTRAINT `customer_id`
    FOREIGN KEY (`customer_id`)
    REFERENCES `CUSTOMER` (`id`),
  CONSTRAINT `product_id`
    FOREIGN KEY (`product_id`)
    REFERENCES `PRODUCT` (`id`));

Insert data in CUSTOMER table

INSERT INTO `CUSTOMER` (`id`, `name`) VALUES ('1', 'Jon Snow');
INSERT INTO `CUSTOMER` (`id`, `name`) VALUES ('2', 'Daenerys Targaryen');
INSERT INTO `CUSTOMER` (`id`, `name`) VALUES ('3', 'Sansa Stark');
INSERT INTO `CUSTOMER` (`id`, `name`) VALUES ('4', 'Arya Stark');
INSERT INTO `CUSTOMER` (`id`, `name`) VALUES ('5', 'Jorah Mormont');
INSERT INTO `CUSTOMER` (`id`, `name`) VALUES ('6', 'Bronn of the Blackwater');

Insert data in PRODUCT table

INSERT INTO `PRODUCT` (`id`, `name`, `price`) VALUES ('1', 'Dragon', '5000');
INSERT INTO `PRODUCT` (`id`, `name`, `price`) VALUES ('2', 'Castle', '1000');
INSERT INTO `PRODUCT` (`id`, `name`, `price`) VALUES ('3', 'Sword', '5');

Insert data in ORDER table

INSERT INTO `ORDER` (`id`, `date`, `customer_id`, `product_id`, `quantity`) VALUES ('1', '2019-01-08 00:00:00', '2', '1', '3');
INSERT INTO `ORDER` (`id`, `date`, `customer_id`, `product_id`, `quantity`) VALUES ('2', '2019-01-22 00:00:00', '6', '3', '1');
INSERT INTO `ORDER` (`id`, `date`, `customer_id`, `product_id`, `quantity`) VALUES ('3', '2019-02-15 00:00:00', '6', '2', '1');
INSERT INTO `ORDER` (`id`, `date`, `customer_id`, `product_id`, `quantity`) VALUES ('4', '2019-02-16 00:00:00', '1', '3', '1');

Database tables

And now that’s what we have in our tables:

CUSTOMER table

CUSTOMER table

 

PRODUCT table

PRODUCT table

 

ORDER table

Outer join tables

Now, let us join these tables using OUTER JOIN

This query returns customer details, purchase date and quantity

SELECT C.id, C.name, O.date, O.quantity
FROM `CUSTOMER` C
FULL JOIN `ORDER` O
ON C.id = O.customer_id;

NOTE: MySQL does not support outer joins, but you can still achieve the same result by using UNION ALL as shown below:

SELECT C.id, C.name, O.date, O.quantity
   FROM `CUSTOMER` C
   LEFT JOIN `ORDER` O
   ON C.id = O.customer_id
UNION ALL
   SELECT C.id, C.name, O.date, O.quantity
   FROM `CUSTOMER` C
   RIGHT JOIN `ORDER` O
   ON C.id = O.customer_id;
Outer join result set

Outer join result set

Disclaimer: The example shown above has been tested with MySQL. Depending on your SQL database the CREATE TABLE syntax may vary.

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