SQL LEFT JOIN

SQL LEFT JOIN (or LEFT OUTER JOIN) is a type of JOIN that returns all the rows from the left table and the matching rows from the right table. If there are no matching rows in the right table, the result will contain NULL values for those columns.

The basic syntax of an SQL LEFT JOIN query is as follows:

SELECT column1, column2, ...
FROM table1
LEFT JOIN table2
ON table1.column = table2.column;

Here, table1 and table2 are the tables that you want to join, column1, column2, and so on are the columns that you want to select, and column is the related column between the two tables.

For example, the following SQL query uses a LEFT JOIN to combine data from two tables:

SELECT customers.customer_name, orders.order_date
FROM customers
LEFT JOIN orders
ON customers.customer_id = orders.customer_id;

In this example, the query joins the customers table and the orders table based on the customer_id column, and selects the customer_name and order_date columns. If a customer has no orders, the result will contain NULL values for the order_date column.

LEFT JOINs are useful when you want to include all the rows from the left table in your result set, even if there are no matching rows in the right table. They can be very powerful and flexible, but they can also be complex and difficult to write correctly. It's important to understand how LEFT JOINs work and to test your queries carefully to ensure that they return the results you expect.