You have a database named DB1 that has the following: --- a Table named Customers that contains a list of customers ---- a table named Invoice that contains invoice information. There is foreign key r

An optional parameter is designed to handle a single, potentially absent, value, not a dynamic collection or 'unlimited list' of multiple values.

While a table-valued parameter effectively passes an unlimited list of customers to a stored procedure, it focuses on the input mechanism rather than the crucial performance optimization required for efficient retrieval, which is addressed by indexing.

To efficiently retrieve invoices for a potentially large, 'unlimited' list of customer IDs, a nonclustered index on the relevant foreign key column (e.g., `CustomerID` in the `Invoice` table) is crucial for optimizing join operations and filter conditions, ensuring acceptable performance for the stored procedure when processing many customers.

Multiple Active Result Sets (MARS) is a feature allowing multiple outstanding data requests on a single connection and is unrelated to defining or passing parameter lists to a stored procedure.