PHP DB Connections & Select operations

I am looking for some guidance on best practice wrt DB operations in a PHP dynamic web site.

To be clear, this web site makes no changes to the data (that happens elsewhere).

It seems to me there are four distinct operations.

  • Defining the DB Connection
  • Opening the DB Connection
  • Selecting data from the DB
  • Closing the DB Connection

The question is when (in the flow of building each page) to perform each of them.

It’s not really a question of performance, I’ve tried Open once and Open for every select, there seems to be negligible impact on performance (although I’ve not tried to measure at scale). Rather it’s a question of best practice for future code maintenance.

Thank you.