Welcome to Westonci.ca, the ultimate question and answer platform. Get expert answers to your questions quickly and accurately. Discover a wealth of knowledge from professionals across various disciplines on our user-friendly Q&A platform. Our platform offers a seamless experience for finding reliable answers from a network of knowledgeable professionals.

Why is it necessary for each "group by" expression in SQL to include at least one column that is not an outer reference? Explain the significance of this requirement in the context of SQL queries and data aggregation.