1 through 5 all essentially amount to this: if the WHERE constraint indicates a contiguous subsequence of the index... or a small list of such subsequences...

1 through 5 all essentially amount to this: if the WHERE constraint indicates a contiguous subsequence of the index... or a small list of such subsequences... and btw we're mildly clever about reparsing your constraint to try to find a way to make it into a small list of contiguous subsequences. It helps to imagine the rows (or rather the index entries sitting in order in a file, and considering where the wanted rows would sit in that file.