[jdoliner]

An optimizer can be right most of the time but it's basically impossible to have it be right all of the time. It really depends on what you're doing as to which approach you prefer. If you absolutely need a query to have a certain performance characteristic then you can't count on the optimizer to get it right a human needs to think through exactly how they want this query to run to ensure it behaves correctly.

There definitely are several use cases where people are willing to sacrifice a risk of misoptimization in exchange for shorter code and we fully intend to support that (it's a complicated project though so we don't now.) However I disagree that having this logic in the app makes it more fragile. Having the precise semantics expressed in the application means you always know exactly how a query is going to be performed. We know this execution plan isn't going to change based on seemingly unrelated properties of the data (as it does with optimizers.) If fragility is the propensity to break then I'd argue having the optimizer in control rather than the developer gives you more fragility than less.