MySQL Error: Expression #3 Not in GROUP BY Clause - 'only_full_group_by' Mode

This error message indicates that your query is trying to group by certain columns, but one of the columns in the SELECT statement is not included in the GROUP BY clause and is not an aggregated column.

To resolve this error, you can either:

1. Add the non-grouped column to the GROUP BY clause: This ensures that the query only retrieves data where all the columns in the SELECT statement are identical.
2. Use an aggregate function on the non-grouped column in the SELECT statement: Aggregate functions like SUM(), AVG(), MAX(), MIN(), etc., summarize data within groups.
3. Disable the 'only_full_group_by' SQL mode: This allows you to select non-grouped columns without adding them to the GROUP BY clause. You can achieve this by modifying the MySQL configuration or by running the following query before executing your actual query:

SET sql_mode=(SELECT REPLACE(@@sql_mode,'ONLY_FULL_GROUP_BY',''));

By implementing one of these solutions, you can resolve the 'Expression #3 of SELECT list is not in GROUP BY clause' error and ensure your query functions correctly.