SQL joins
by Yogi P - December 15, 2022
Types of SQL Joins
In SQL, a join is a way to combine data from multiple tables based on a common field between them. This allows you to retrieve data from multiple tables with a single query and organize it in a meaningful way.
There are several types of joins in SQL, including:
INNER JOIN: This type of join returns only rows that have matching values in both tables.
LEFT JOIN: This type of join returns all rows from the left table, even if there are no matching values in the right table.
RIGHT JOIN: This type of join returns all rows from the right table, even if there are no matching values in the left table.
FULL JOIN: This type of join returns all rows from both tables, even if there are no matching values.
Joins are typically used in SQL queries to retrieve data from multiple tables and combine it in a meaningful way.
For example, if you have a customer table and an orders table, you could use a join to retrieve the customer’s name and the details of their orders in a single query.
This can be useful for generating reports, analyzing data, or other tasks that require data from multiple tables.
INNER JOIN in SQL
In SQL, an INNER JOIN is a type of join that is used to combine data from two or more tables based on a common field between them. This type of join returns only rows that have matching values in both tables.
For example, consider a scenario where you have a customers table and an orders table. The customers table contains data about your customers, such as their name and contact information. The orders table contains data about the orders that your customers have placed, such as the order date, the products that were ordered, and the total amount.
SELECT customers.name, customers.email, customers.phone
FROM customers
INNER JOIN orders ON customers.id = orders.customer_id;
This query will return only the rows from the customers table that have matching values in the orders table (i.e., customers who have placed an order). The result of this query would be a table that contains the name, email, and phone number of each customer who has placed an order.
INNER JOINs are often used when you want to retrieve data from multiple tables and only include rows that have matching values in both tables. This allows you to combine data from multiple tables and organize it in a meaningful way.
OUTER JOIN
In SQL, an outer join is a type of join that is used to combine data from two or more tables based on a common field between them. Unlike an inner join, which only returns rows that have matching values in both tables, an outer join returns all rows from one table and only the matching rows from the other table.
There are two types of outer joins in SQL: LEFT OUTER JOIN and RIGHT OUTER JOIN. A LEFT OUTER JOIN returns all rows from the left table and only the matching rows from the right table. A RIGHT OUTER JOIN returns all rows from the right table and only the matching rows from the left table.
For example, consider a scenario where you have a customers table and an orders table. The customers table contains data about your customers, such as their name and contact information. The orders table contains data about the orders that your customers have placed, such as the order date, the products that were ordered, and the total amount.
To retrieve the name and contact information of all customers, along with the details of their orders (if any), you could use the following LEFT OUTER JOIN query:
SELECT customers.name, customers.email, customers.phone, orders.order_date, orders.total_amount
FROM customers
LEFT OUTER JOIN orders ON customers.id = orders.customer_id;
This query will return all rows from the customers table, along with only the matching rows from the orders table (i.e., the orders that have been placed by the customers). The result of this query would be a table that contains the name, email, and phone number of each customer, along with the details of their orders (if any).
Outer joins are often used when you want to combine data from two tables and include all rows from one table, along with only the matching rows from the other table. This can be useful for generating reports, analyzing data, or other tasks that require data from multiple tables.
LEFT JOIN
In SQL, a LEFT JOIN is a type of join that is used to combine data from two or more tables based on a common field between them. This type of join returns all rows from the left table, even if there are no matching values in the right table.
For example, consider a scenario where you have a customers table and an orders table. The customers table contains data about your customers, such as their name and contact information. The orders table contains data about the orders that your customers have placed, such as the order date, the products that were ordered, and the total amount.
To retrieve the name and contact information of all customers, along with the details of their orders (if any), you could use the following LEFT JOIN query:
SELECT customers.name, customers.email, customers.phone, orders.order_date, orders.total_amount
FROM customers
LEFT JOIN orders ON customers.id = orders.customer_id;
This query will return all rows from the customers table, even if there are no matching values in the orders table (i.e., customers who have not placed any orders). The result of this query would be a table that contains the name, email, and phone number of each customer, along with the details of their orders (if any).
LEFT JOINs are often used when you want to combine data from two tables and include all rows from the left table, even if there are no matching values in the right table. This can be useful for generating reports, analyzing data, or other tasks that require data from multiple tables.
RIGHT JOIN
In SQL, a RIGHT JOIN is a type of join that is used to combine data from two or more tables based on a common field between them. This type of join returns all rows from the right table, even if there are no matching values in the left table.
For example, consider a scenario where you have a customers table and an orders table. The customers table contains data about your customers, such as their name and contact information. The orders table contains data about the orders that your customers have placed, such as the order date, the products that were ordered, and the total amount.
To retrieve the details of all orders, along with the name and contact information of the customer who placed the order (if any), you could use the following RIGHT JOIN query:
SELECT customers.name, customers.email, customers.phone, orders.order_date, orders.total_amount
FROM customers
RIGHT JOIN orders ON customers.id = orders.customer_id;
RIGHT JOINs are often used when you want to combine data from two tables and include all rows from the right table, even if there are no matching values in the left table. This can be useful for generating reports, analyzing data, or other tasks that require data from multiple tables.
FULL JOIN
In SQL, a FULL JOIN is a type of join that is used to combine data from two or more tables based on a common field between them. This type of join returns all rows from both tables, even if there are no matching values.
For example, consider a scenario where you have a customers table and an orders table. The customers table contains data about your customers, such as their name and contact information. The orders table contains data about the orders that your customers have placed, such as the order date, the products that were ordered, and the total amount.
To retrieve the name and contact information of all customers, along with the details of their orders (if any), you could use the following FULL JOIN query:
SELECT customers.name, customers.email, customers.phone, orders.order_date, orders.total_amount
FROM customers
FULL JOIN orders ON customers.id = orders.customer_id;
FULL JOINs are often used when you want to combine data from two tables and include all rows from both tables, even if there are no matching values. This can be useful for generating reports, analyzing data, or other tasks that require data from multiple tables.
Difference between INNER JOIN and OUTER JOIN
INNER JOIN |
OUTER JOIN |
|---|---|
| INNER JOINs are used to return only those rows that have matching values in the tables being joined. This means that the resulting table will only include rows where there is a match in both tables. | An OUTER JOIN, on the other hand, is a type of JOIN that is used to combine the data from two or more tables, even if there is no matching value in one or more of the tables. |
| INNER JOINs only return rows that have matching values in the joined tables | OUTER JOINs return all the rows from at least one of the tables, even if there are no matching values in the other table(s). |
Difference between INNER JOIN and FULL JOIN
The main difference between INNER JOIN and FULL JOIN in SQL is the way they combine data from multiple tables. INNER JOIN only returns rows that have matching values in both tables, while FULL JOIN returns all rows from both tables, even if there are no matching values.
For example, consider a scenario where you have a customers table and an orders table. The customers table contains data about your customers, such as their name and contact information. The orders table contains data about the orders that your customers have placed, such as the order date, the products that were ordered, and the total amount.
SELECT customers.name, customers.email, customers.phone
FROM customers
INNER JOIN orders ON customers.id = orders.customer_id;
This query will return only the rows from the customers table that have matching values in the orders table (i.e., customers who have placed an order). The result of this query would be a table that contains the name, email, and phone number of each customer who has placed an order.
To retrieve the name and contact information of all customers, along with the details of their orders (if any), you could use the following FULL JOIN query:
SELECT customers.name, customers.email, customers.phone, orders.order_date, orders.total_amount
FROM customers
FULL JOIN orders ON customers.id = orders.customer_id;
As you can see, INNER JOIN and FULL JOIN produce different results depending on how they combine data from the tables. INNER JOIN only returns rows that have matching values in both tables, while FULL JOIN returns all rows from both tables, even if there are no matching values.
Difference between LEFT JOIN and RIGHT JOIN
The main difference between LEFT JOIN and RIGHT JOIN in SQL is the way they combine data from multiple tables. LEFT JOIN returns all rows from the left table, even if there are no matching values in the right table, while RIGHT JOIN returns all rows from the right table, even if there are no matching values in the left table.
For example, consider a scenario where you have a customers table and an orders table. The customers table contains data about your customers, such as their name and contact information. The orders table contains data about the orders that your customers have placed, such as the order date, the products that were ordered, and the total amount.
To retrieve the name and contact information of all customers, along with the details of their orders (if any), you could use the following LEFT JOIN query:
SELECT customers.name, customers.email, customers.phone, orders.order_date, orders.total_amount
FROM customers
LEFT JOIN orders ON customers.id = orders.customer_id;
This query will return all rows from the customers table, even if there are no matching values in the orders table (i.e., customers who have not placed any orders). The result of this query would be a table that contains the name, email, and phone number of each customer, along with the details of their orders (if any).
To retrieve the details of all orders, along with the name and contact information of the customer who placed the order (if any), you could use the following RIGHT JOIN query:
SELECT customers.name, customers.email, customers.phone, orders.order_date, orders.total_amount
FROM customers
RIGHT JOIN orders ON customers.id = orders.customer_id;
This query will return all rows from the orders table, even if there are no matching values in the customers table (i.e., orders that have not been placed by any customers). The result of this query would be a table that contains the details of each order, along with the name, email, and phone number of the customer who placed the order (if any).
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