I am writing a fairly simple webapp that pulls data from 3 tables in a mysql database. Because I don’t need a ton of advanced filtering it seems theoretically faster to construct and then work within large multi-dimensional arrays instead of doing a mysql query whenever possible.
In theory I could just have one query from each table and build large arrays with the results, essentially never needing to query that table again. Is this a good practice, or is it better to just query for the data when it’s needed? Or is there some kind of balance, and if so, what is it?
PHP arrays can be very fast, but it depends on how big are those tables, when the numbers get huge MySQL is going to be faster because, with the right indexes, it won’t have to scan all the data, but just pick the ones you need.
I don’t recommend you to try what you’re suggesting, MySQL has a query cache, so repeated queries won’t even hit the disk, so in a way, the optimization you’re thinking about is already done.
Finally, as Chris said, never think about optimizations when they are not needed.
About good practices, a good practice is writing the simplest (and easy to read) code that does the job.
If in the end you’ll decide to apply an optimization, profile the performance, you might be surprised, by unexpected results.