I wanted to surface a discussion in [1] regarding the expected behavior of GROUP BY with VOLATILE expressions. There seems to be a discrepancy between how volatile functions (RANDOM(), also confirmed with TIMEOFDAY()) and subqueries are evaluated in groups. In the examples below, volatile functions do not always appear to be evaluated per-call (evidenced by looking at EXPLAIN or results) whereas scalar subqueries always appear to be independently evaluated.
Based on the docs, "A query using a volatile function will re-evaluate the function at every row where its value is needed," it seems that the handling of subqueries is correct and that each call to RANDOM() should be evaluated (not the current behavior). But, what is correct/anticipated?
The observed behaviors are unlikely to change. Prior discussions can be found regarding this:
