You test it.
And what do you mean by “know SQL?” No one knows everything about SQL. Virtually everyone writing SQL is in between the two extreme cases you provide.
Like I said, you need to test it. Not read it. Test it.
I usually find ChatGPT very good for converting conceptual ideas to a concrete piece of 'boilerplate' to work off of. It can help you jump gaps in your proces, but in the end you still have to make the jumps yourself.
It is the same with googling, looking for a solution on StackOverflow: understanding/judging whether the solution is good may be faster than constructing it yourself.