Left Join - (MariaDB Joins)

The left join is a type of join used in database queries to combine data from two tables based on a common column, allowing for the selection of data from both tables. In MariaDB, the left join is performed using the LEFT JOIN keyword.

Syntax

The syntax for performing a left join in MariaDB is as follows:

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

Here, table1 and table2 are the names of the tables being joined, column_name is the column being used for the join, and column_name(s) are the columns being selected for output.

Example

Here is an example of using a left join to combine data from two tables:

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

Output

Executing the SQL statement will retrieve all orders, including those without a matching customer record, along with the customer name (if available) and order date.

Explanation

In the above SQL code, we are selecting all order_id, customer_name, and order_date records from both the orders and customers tables where the customer_id column matches. This is done using a LEFT JOIN, which retrieves all records from the left-hand table (orders) and matching records from the right-hand table (customers). If there is no matching record in the right-hand table, the corresponding fields in the result set will be null.

Use

Left joins are commonly used in database queries to retrieve data from two tables based on a common column. This can be useful when working with large data sets or data where some records may be missing data. In addition, left joins can be used in conjunction with other types of joins to further refine the data being retrieved.

Important Points

• A left join is a database join that combines data from two tables based on a common column.
• The left join is performed in MariaDB using the LEFT JOIN keyword.
• Left joins can be useful when working with large data sets or data where some records may be missing data.
• Left joins can be used in conjunction with other types of joins to further refine the data being retrieved.

Summary

In summary, the left join is a type of join used in database queries to combine data from two tables based on a common column. It is performed in MariaDB using the LEFT JOIN keyword and can be useful when working with large data sets or data where some records may be missing data. By combining with other types of joins, left join can further refine the data being retrieved from database tables.