пт, 31 окт. 2025 г. в 00:35, Peter Geoghegan <pg@bowt.ie>:
I didn't understand every nuance of row compare inequalities myself until quite recently. The rules with NULLs are particularly tricky.
It seems worthwhile to clear things up now in large part due to the recent addition of code in places like _bt_advance_array_keys -- code that wants to to treat row compare keys as if they were just a simple scalar inequality on the row compare's most significant column. That general behavior isn't new (e.g., _bt_first has long ignored row compare scan key markings when deducing a NOT NULL constraint), but it's not easy to see why it's correct.
Greetings.
I took a look at the patch. Proposed comments look highly valuable, especially around NULLs, doesn't look immediately obvious, so definitely requires a comment.
