These are both great observations. VOLATILE/STABLE/IMMUTABLE is definitely a choice worth considering and making in an educated way when writing a function. A

These are both great observations. VOLATILE/STABLE/IMMUTABLE is definitely a choice worth considering and making in an educated way when writing a function. Also, using WITH to create CTEs makes SQL easy to read, but sometimes will slow down a query considerably. I have a feeling that new releases will make attempts to mitigate this issue in some cases.