In this lesson we’ll look at the alternative approach to solve the problem from the previous lesson. Namely, select the very first account for each user.
Imagine, if accounts table would have an index for each account per user. That way we’d just select all accounts where index equals to 1.
Turns out SQL has a special functionality for such calculation. It’s called window functions.
We’ve already met two type of functions.
Scalar functions accept one or more values as an input and return one or more values as an output. For...