[zenmac]

>I think a stored generated column allows you to create an index on it directly. Isn't it better approach?

Is it also possible to create index (maybe partial index) on expressions?

[masklinn]

That's the first solution (a function based index), however it has the drawback of fragility: a seemingly innocent change to the query can lead to not matching the index's expression anymore). Which is why the article moves on to generated columns.