This is not really an answer to your question, but it sounds like you have PHP developers trying to become part time database developers. I don't mean this nega

This is not really an answer to your question, but it sounds like you have PHP developers trying to become part time database developers. I don't mean this negatively, just that server-side developers are different from database devs which are different from UI/front-end devs. Once you get beyond normal queries and enter the realm of real database development you likely want someone who is a genuine database developer. I'm worked with several database developers plus my wife is a database developer. They are a different breed, and they really develop applications in the data layer. I can say from experience that once you add a database developer you'll never look at the data layer the same. Often, there is a substantial amount of work that can be performed better by the database (whether it's Oracle, SQL Server, Postgres or whatever) since they have 30+ years of tuning for specific data operations.