detect cartesian product or other non sensible queries

I'm working on a product which gives users a开发者_JS百科 lot of "flexibility" to create sql, ie they can easily set up queries that can bring the system to it's knees with over inclusive where clauses.

I would like to be able to warn users when this is potentially the case and I'm wondering if there is any known strategy for intelligently analysing queries which can be employed to this end?

I feel your pain. I've been tasked with something similar in the past. It's a constant struggle between users demanding all of the features and functionality of SQL while also complaining that it's too complicated, doesn't help them, doesn't prevent them from doing stupid stuff.

Adding paging into the query won't stop bad queries from being executed, but it will reduce the damage. If you only show the first 50 records returned from SELECT * FROM UNIVERSE and provide the ability to page to the next 50 and so on and so forth, you can avoid out of memory issues and reduce the performance hit.

I don't know if it's appropriate for your data/business domain; but I forcefully add table joins when the user doesn't supply them. If the query contains TABLE A and TABLE B, A.ID needs to equal B.ID; I add it.

If you don't mind writing code that is specific to a database, I know you can get data about a query from the database (Explain Plan in Oracle - http://www.adp-gmbh.ch/ora/explainplan.html). You can execute the plan on their query first, and use the results of that to prompt or warn the user. But the details will vary depending on which DB you are working with.