Column(s) to create index for: - Employee_no Why these column(s): Creating an index on the Employee_no column would be beneficial for optimizing the query. Since the query filters the records based on the Employee_no column in both the outer and inner queries, an index on this column can significantly improve the performance by allowing efficient lookup and retrieval of the matching rows. Explanation of what the SQL query does: The SQL query retrieves all columns (*) from the Employee table where the rowid of a record in table a is equal to the maximum rowid returned by a subquery. The subquery calculates the maximum rowid from the Employee table for each Employee_no and compares it with the rowid in the outer query. Essentially, the query aims to retrieve the latest row for each distinct Employee_no. To optimize this query, creating an index on the Employee_no column is recommended. However, it's important to evaluate and test the performance impact of the index in your specific database environment and workload.