How to Access Multiple Columns in Join Queries with Different Join Conditions?

Accessing Multiple Columns in Join Queries

When joining tables by different columns, referencing multiple columns can be a common need. Consider a scenario with a user and complaint table, as described in the given context. To retrieve the usernames for both the opening and closing actions in each complaint, we must extend the join query to encompass the necessary columns.

The provided query used a left join to link the complaint and user tables based on the opened_by column. To include the closed_by column, we employ another left join using the user table, aliasing the table references as "A" and "B" to distinguish between the two join conditions.

The resulting query thus becomes:

<code class="sql">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</code>

Through this query, both usernames can be extracted and displayed alongside the complaint text for each record.

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