There are several scenarios in which renaming of attributes is necessary to specify a query unambiguously. Here are some types of queries where attribute renaming becomes essential:

• Self-Joins: When performing self-joins on a table, where the table is joined with itself based on a common attribute, attribute renaming is required to differentiate between the attributes from each instance of the table. By renaming the attributes in the self-join, we can specify the correct attributes to be used in the join condition and projection.

• Aliasing: Aliasing is used to provide a temporary or alternate name to an attribute or table in a query. It is often used to simplify complex queries or to disambiguate attribute names when multiple tables are involved. By providing an alias, we can refer to the attribute using the alias instead of the original attribute name, making the query more readable and avoiding naming conflicts.

• Subqueries: In queries involving subqueries, renaming attributes can be necessary to distinguish between the attributes in the outer query and the attributes in the subquery. This is especially true when subqueries return a result set with the same attribute names as the outer query. By renaming attributes, we can specify which attributes are being used in the main query and which ones are from the subquery.

• Aggregate Functions: In queries that involve aggregate functions like SUM, AVG, MAX, etc., renaming attributes can be useful when specifying the attributes to be aggregated. For example, if multiple tables are joined, and both tables have attributes with the same name, renaming the attributes helps specify which attributes are to be aggregated.

• Ambiguous Attribute Names: When a query involves multiple tables that have attributes with the same name, renaming the attributes can avoid ambiguity and ensure that the correct attributes are referenced in the query. By providing unique names to the attributes, we can clearly specify the intended attributes in the query.