Multiple prepared statements, keep alive until finish page

Question

Lets say a have Web page with some classes. One is loaded Mysqli connect it to DB at the beginning and keep connected. Now question is:

Is good solution make in (example setting class) prepared statement for calling value from DB table 'settings' and keep it open (statement) until finish (at footer close statement and connection) or just load all data from 'settings' DB table to array() in php and just call it from array not binding it from DB.

Second question is if I have statement open may I open another statement for another class (example class for calling text from DB) and do it same like in previous example? And than, of course close it at finish page.

Is there any performance or security problem, you can see there...

Answer 1

1. As far as I know, nobody is doing it this way. Mostly because the real benefit from the multiple execution is not that grand as some imagine, and just doesn't worth the trouble. For the short primary key lookups run in small numbers (several dozens at max) you'll hardly be able to tell the difference.
   (However, there are no arguments against such practice either - you can make it this way, with single statement prepared/multiple executions, if you wish).

2. Yet single query that is fetching no more than couple hundreds of records still would be faster than separate queries (even prepared) to get the same amount. So, as long as your settings keep at moderate amount, it's better to get them all at once.

3. Yes, of course you can have as many statements prepared as you need.
   (The only problem could be with fetching results. You have to always get_result/store_result, to make sure there are no results left pending and preventing other queries to run, either regular or prepared).

Answer 2

The statement executes as one SQL statement over your DB connection. It's not going to keep going back to the database and grabbing a single row one at a time, so don't worry about that.

In general, you should be loading everything into some data structure. If your query is returning more data than you need, then that's something you need to fix in your query. Don't run SQL that returns a huge set of data, then rely on PHP to go through it row by row and perform some hefty operations on it. Just write SQL that gets what you need in the first place. I realize this isn't always possible, but when people talk about optimizing their website, query optimization is usually at/near the top of that list, so it's pretty important.

You're definitely supposed to execute multiple statements. It's silly to keep opening and closing entire db connections before getting any data.