You wrote the query in an afternoon. It ran against your development database in four milliseconds, the test suite went green, and you shipped it. Six weeks later, someone in support forwards a screen...
Your app was fast for a year. Nothing changed — same code, same server, same query you wrote in an afternoon and never thought about again. Then one Tuesday the orders page takes eleven seconds to loa...
You wrote a query to list your customers and their orders. It ran fine — but half your customers vanished from the results. The ones who never placed an order simply weren't there. Nothing errored, no...
