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A question: Does anyone know how well AI does generating performative SQL in years-old production databases? In terms of speed of execution, locking, accuracy, etc.?

I see the promise for green-field projects.

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It's very hit or miss. Claude does OK-ish, others less so. You have to explicitly state the DB and version, otherwise it will assume you have access to functions / features that may not exist. Even then, they'll often make subtle mistakes that you're not going to catch unless you already have good knowledge of your RDBMS. For example, at my work we're currently doing query review, and devs have created an AI recommendation script to aid in this. It recommended that we create a composite index on something like `(user_id, id)` for a query. We have MySQL. If you don't know (the AI didn't, clearly), MySQL implicitly has a copy of the PK in every secondary index, so while it would quite happily make that index for you, it would end up being `(user_id, id, id)` and would thus be 3x the size it needed to be.

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