SQL Query to Return Multiple Data from Inner Join

Understanding the Problem

The problem presents a scenario where we have two database tables: users_account and chatroom_message. The goal is to retrieve users who have received chat messages in the chatroom_message table. However, instead of showing the active user’s name as shown in the provided SQL query, we want to display the party user’s name.

Table Structure

To better understand the problem, let’s first examine the table structure:

Users Account Table

Chatroom Message Table

Current SQL Query

The provided SQL query attempts to achieve the desired result but has an issue:

SELECT * FROM chatroom_message cm
INNER JOIN users_account ua ON cm.userid_a = ua.reg_userid 
WHERE cm.userid_a = :chat_client
UNION ALL
SELECT * FROM chatroom_message cm
INNER JOIN users_account ua ON cm.userid_b = ua.reguserid 
WHERE cm.userid_b = :chat_client

This query joins the chatroom_message table with the users_account table on both userid_a and userid_b. However, it only returns rows where userid_a or userid_b matches the active user’s ID. As a result, the party user’s name is not included in the output.

Desired Result

We want to modify the SQL query to return users who have received chat messages from either party. The desired output should display the party user’s name for each active user.

Solution

To achieve this, we need to use a different approach. Instead of joining on userid_a and userid_b, we can join on both columns in the WHERE clause. However, since we want to return users who have received messages from either party, we should use a combination of OR and UNION ALL.

Here’s the modified SQL query:

SELECT ua.reg_userid, ua.name AS party_user_name
FROM chatroom_message cm
INNER JOIN users_account ua ON (cm.userid_a = ua.reguserid OR cm.userid_b = ua.reguserid)
WHERE cm.userid_a = :chat_client
UNION ALL
SELECT ua.reg_userid, ua.name AS party_user_name
FROM chatroom_message cm
INNER JOIN users_account ua ON (cm.userid_a = ua.reguserid OR cm.userid_b = ua.reguserid)
WHERE cm.userid_b = :chat_client

In this modified query:

• We use a subquery to check if either userid_a or userid_b matches the active user’s ID in both inner joins.
• We join on both columns using the OR operator.
• We use the AS keyword to assign an alias (party_user_name) to the name column.

Example Output

Let’s assume the active user’s ID is 1 (Peter). The modified query would return:

For Peter, since he has received messages from both parties, the output will display his contact chat list. Similarly, for the active user with ID 2 (John), the output will show Peter as his chat partner.

Conclusion

The modified SQL query addresses the issue by joining on both columns and using a combination of OR and UNION ALL. This approach ensures that users who have received messages from either party are correctly identified, along with their corresponding party user’s name.

Last modified on 2025-04-06