SUM for strings in Oracle

At times I have needed in an aggregate function to build a list of varchar values in single row inside a group. Something like SUM aggregate function but for strings. I wanted to have for each group a list of strings separated by defined delimiter.

NO_DATA_FOUND is not raised from a function in Oracle SQL

It's not a bug, it's an Oracle feature. It happens with NO_DATA_FOUND exception only. And such behaviour is typical for all version of database. It is not documented anywhere in Oracle documentation. Just remeber and keep it in mind.

Now I show what I am talking about.

Oracle NVL vs COALESCE

Now I try to accumulate all my knowledge about these similar functions.
NVL is native Oracle function whereas COALESCE is ANSI SQL one.