A question about efficientcy

[apzer0]

Is one query always better then two even if the query is very complex?

[AstroTeg]

Too many variables to answer this question with a yes or a no. It depends on the database engine, your database structure, and your query.

In my experiences with MySQL, I've found a handful of simple queries beat a monster join query. But in MS SQL, if you tweaked the query and tables, one query would be a lot faster than several little queries.

Your mileage will vary. If performance is a serious issue, then test both approaches with your application and determine which works best for you.

[apzer0]

Thanks, any other opinions?
I'm using mysql datatbase.
The reason i'm asking is because i'm working on a kindda big project and made two pretty big querys. Suddnly I thought of a way to join the two into one huge query and started thinking which is better.

By the way, how do you check how much time a query take? Like the normal mktime() check?

[Sxooter]

What's fast in one database may be murderously slow in another, and vice versa.

The only way to KNOW which is faster is to build a test case and test it.

Generally, the more complex the query, the faster PostgreSQL runs it, and the slower MySQL tends to run it, but this isn't always true. Each query planner in a database makes different choices about how to execute the query, and has different optimizations for different corner cases.