DB View performance

I have a relatively complicated database view that references other views. Back in 2020, I was able to create some indexes to improve performance when this view was used.

Without going into a lot of detail, I added a column to the view to simply count the lines in the primary table (the view already groups results). I did this generating the DDL from ACS Schemas tool. Using run sql scripts, I did a "create or replace view" after adding the column. This change killed the performance, so I removed the new column and ran "create or replace view" again.

Now to the odd part... the performance was still horrible. I didn't know what to do, so I restored the view from our cloud backup - this fixed the performance issue.

My question is why? What is happening behind the scene that I'm not considering?
I honestly can't imagine that adding a "count(myfield) as mynewfield" column would dramatically affect the performance.

Greg
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