How to Efficiently Join the Same Table Multiple Times on Different Columns for User Information Retrieval?

Joining the Same Table Twice on Different Columns for Versatile User Information Retrieval

This query aims to retrieve usernames for both the opened_by and closed_by columns in the complaint table, where the users are stored in the user table. The challenge lies in joining the user table multiple times using different columns.

To accomplish this task, we employ a LEFT JOIN operation for each instance of the user table, aliasing the joined tables as A and B for clarity. The query proceeds as follows:

SELECT
     complaint.complaint_text,
     A.username,
     B.username
FROM
     complaint
     LEFT JOIN user A ON A.user_id=complaint.opened_by
     LEFT JOIN user B ON B.user_id=complaint.closed_by

In this query, we start by selecting the complaint_text column from the complaint table and the usernames from the user table for both the opened_by and closed_by columns.

We then join the complaint table with the user table based on the opened_by column using LEFT JOIN. This allows us to match the user_id from complaint.opened_by to the user_id in the user table and retrieve the corresponding username. We alias the joined table as A.

Next, we perform another LEFT JOIN operation between the complaint table and the user table based on the closed_by column. We alias this joined table as B.

The result of this query provides a clear view of the complaint details, along with the usernames of both the complainant and the resolved By columns.

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