Re: Select last row that is less than or equal to a date

[Rick James]

Øystein, I have long suspected that the optimizer is less than optimal in the compound-index + DESC case:
INDEX(a,b)
WHERE a=1 ORDER BY b DESC
The equivalent ASC code seems to be optimized, but the DESC case seems to fail to "jump to the end of a=1, then read backwards".

I don't know whether the "AND b < 123" factors into the issue.

Whenever I suspect this, I realize that there aren't enough rows to worry about, and I move on to other issues. (I first suspected this in the 4.0 days.)

Good luck.