If I should optimize only one query, which one should it be ?
Answering this question is not easy. Like always, the best response is “it depends” !
But let’s try to give you all the necessary info the provide the most accurate answer. Also, may be fixing one single query is not enough and looking for that specific statement will lead in finding multiple problematic statements.
In the evening I read MySQL 8.0: if I should optimize only one query on my application, which one should it be ?.