I don't think there's any perfect universal answer for this. I only have a few things I've done that work. Rails for Ruby comes with some pretty nice setups fo

I don't think there's any perfect universal answer for this. I only have a few things I've done that work. Rails for Ruby comes with some pretty nice setups for testing the database code. There's a test DB by default with the same schema as Production, and the usual test frameworks (FactoryBot and RSpec) make it easy to set up some data in the actual DB for each spec, run model code that makes actual SQL queries, and assert against the results. I would have hoped most other web hosting frameworks would make as much effort to making it straightforward to test your database code, but it doesn't really seem to be the case. In Rust, there's a very handy crate called sqlx. What it does is, at compile time, it runs all of the SQL in your codebase against a copy of your database to both validate that it runs without errors and map the input and output types to typecheck the Rust code. When it comes to stuff like validating that your queries are performant against production datasets or that there isn't any unexpected data in production that breaks your queries, well I pretty much got nothing. Maybe try a read replica to execute against?