SQL LEFT JOIN

In this tutorial, we'll learn about SQL LEFT JOIN with the help of examples.

The SQL LEFT JOIN joins two tables based on a common column, and selects records that have matching values in these columns and remaining rows from the left table.

Example

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
LEFT JOIN Orders
ON Customers.customer_id = Orders.customer;

Here's how this code works:

How to use LEFT JOIN in SQL
Example: SQL LEFT JOIN

Here, the SQL command selects customer_id and first_name columns (from the Customers table) and the amount column (from the Orders table).

And, the result set will contain those rows where there is a match between customer_id (of the Customers table) and customer (of the Orders table) along with all the remaining rows from the Customers table.


Syntax of LEFT JOIN

The syntax of LEFT JOIN is:

SELECT columns
FROM table1
LEFT JOIN table2
ON table1.column_name = table2.column_name;

LEFT JOIN With WHERE Clause

The SQL command can have an optional WHERE clause with the LEFT JOIN statement. For example,

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
LEFT JOIN Orders
ON Customers.customer_id = Orders.customer
WHERE Orders.amount >= 500;

Here, the SQL command joins two tables and selects rows where the amount is greater than or equal to 500.


SQL LEFT JOIN With AS Alias

We can use AS aliases inside LEFT JOIN to make our snippet short and clean. For example,

SELECT C.category_name, P.product_title
FROM Category AS C
LEFT JOIN Products AS P
ON C.category_id = P.cat_id;

Here, the SQL command selects common rows between Category and Products table.


Left Join Vs Other Joins

LEFT JOIN Vs LEFT OUTER JOIN

We can also use LEFT OUTER JOIN instead of LEFT JOIN. Basically, these two clauses are the same.

That means,

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
LEFT JOIN Orders
ON Customers.customer_id = Orders.customer;

is similar to

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
LEFT OUTER Orders
ON Customers.customer_id = Orders.customer;
LEFT JOIN Vs INNER JOIN

The LEFT JOIN selects the common rows as well as all the remaining rows from the left table. Whereas the INNER JOIN selects only the common rows between two tables.

Let's take a look at example,

LEFT JOIN

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
LEFT JOIN Orders
ON Customers.customer_id = Orders.customer;

Output

How to use LEFT JOIN in SQL
Example: SQL LEFT JOIN Output

INNER JOIN

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
INNER JOIN Orders
ON Customers.customer_id = Orders.customer;

Output

How to use INNER JOIN in SQL
Example: SQL INNER JOIN Output
LEFT JOIN Vs RIGHT JOIN

The LEFT JOIN selects the common rows as well as all the remaining rows from the left table. Whereas the RIGHT JOIN selects the common rows as well as all the remaining rows from the right table.

Let's take a look at example,

LEFT JOIN

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
LEFT JOIN Orders
ON Customers.customer_id = Orders.customer;

Output

How to use LEFT JOIN in SQL
Example: SQL LEFT JOIN Output

RIGHT JOIN

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
RIGHT JOIN Orders
ON Customers.customer_id = Orders.customer_id;

Output

How to use RIGHT JOIN in SQL
Example: SQL RIGHT JOIN Output
LEFT JOIN Vs FULL OUTER JOIN

The LEFT JOIN selects the common rows as well as all the remaining rows from the left table. Whereas the FULL OUTER JOIN selects all the rows from both the tables.

Let's take a look at example,

LEFT JOIN

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
LEFT JOIN Orders
ON Customers.customer_id = Orders.customer;

Output

How to use LEFT JOIN in SQL
Example: SQL LEFT JOIN Output

FULL OUTER JOIN

SELECT Customers.customer_id, Customers.first_name, Orders.amount
FROM Customers
FULL OUTER JOIN Orders
ON Customers.customer_id = Orders.customer;

Output

How to use FULL OUTER JOIN in SQL
Example: SQL FULL OUTER JOIN Output

Recommended Readings

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