General rules for simplifying SQL statements?

Question

I'm looking for some "inference rules" (similar to set operation rules or logic rules) which I can use to reduce a SQL query in complexity or size. Does there exist something like that? Any papers, any tools? Any equivalencies that you found on your own? It's somehow similar to query optimization, but not in terms of performance. To state it different: Having a (complex) query with JOINs, SUBSELECTs, UNIONs is it possible (or not) to reduce it to a simpler, equivalent SQL statement, which is producing the same result, by using some transformation rules? So, I'm looking for equivalent transformations of SQL statements like the fact that most SUBSELECTs can be rewritten as a JOIN.

Answer 1

Simplifying SQL statements depend on both physical and logical plans.

Components of a physical plan: Access path selection for each relation – Scan the relation or use an index

Implementation choice for each operator – Nested loop join, hash join, etc

Scheduling decisions for operators – Pipelined execution or intermediate

materialization

Logical plans can include push selection down and join reorder based on the size of tables.

Simplifying SQL statements is not about reducing the length of SQL statements, yet about utilizing optimization algorithm.