Left, Right, or Inner Join: Which SQL Join Type Should You Choose?

Determining the Appropriate Join Type: Left, Right, or Inner

When joining tables in a SQL query, it can be challenging to determine which join type is most suitable. This article explores the differences between left, right, and inner joins and provides guidance on how to make an informed decision.

Usage of SQL JOINS

As stated in the previous article, SQL JOINS are crucial when accessing multiple tables in a SELECT statement and ensuring that only rows with matching records across the joined tables are returned.

Understanding the Different Join Types

• Left JOIN: This type of join returns all rows from the left table (table with the ON clause) and matches them to the corresponding rows in the right table (table with the LEFT JOIN clause). Rows from the right table without corresponding matches in the left table are also included.
• Right JOIN: Similar to a left join, this type returns all rows from the right table and matches them to the corresponding rows in the left table. In this case, rows from the left table without corresponding matches in the right table are also included.
• Inner JOIN: This join type includes only rows that have matching records in both the left and right tables. Rows that do not satisfy the join condition are excluded.

Determining the Appropriate Join Type

The following guidelines can help you decide which join type is most appropriate:

• Left JOIN: Use a left join when you want to retrieve all rows from the left table and any matching rows from the right table.
• Right JOIN: Use a right join when you want to retrieve all rows from the right table and any matching rows from the left table.
• Inner JOIN: Use an inner join when you only want to retrieve rows that have matching records in both tables.

Example Query and Join Type Selection

In the query provided, a left join is used between the "batchDetails" and "folderDetails" tables. This is because we want to retrieve all rows from the "batchDetails" table (left table) and match them to the corresponding rows in the "folderDetails" table (right table). Rows in the "folderDetails" table that do not have corresponding matches in the "batchDetails" table will also be included in the result.

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