This question relates to this post. <br /> <br />I'm not clear on how to tell, by looking at a query, whether it's linear or involves a cross-product. Is that something that requires a deep understanding of SQL, or is there a web page you could point me to that would explain this more fully? (My background is in math, so I'm familiar with the terms "linear" and "cross-product" in other contexts.) <br /> <br />