I was browsing the proceedings of this year's VLDB conference and came across the paper below doing something similar to Cosette (http://cosette.cs.washington.edu/), validating two SQL queries are equivalent. Pairs of queries were pulled from Calcite pre and post-optimization. I've only skimmed the paper, but I don't believe they mention any incorrect rewrites, which is great news :)
http://www.vldb.org/pvldb/vol12/p1276-zhou.pdf -- Michael Mior mm...@apache.org