Comments on: Funny differences between Mysql and Postgresql

By: Joseph Scott

Joseph Scott — Wed, 10 Nov 2004 16:30:19 +0000

As to why MySQL rounds the way it does, that was directly from the MySQL docs. I didn’t really but it either, but it looks like that is their “official” explanation.

By: Scott

Scott — Tue, 09 Nov 2004 17:23:47 +0000

Hmm. Should have tried it BEFORE posting the last comment so as to avoid having to post another. It looks to me like MySQL follows a similar rounding rule, but with even/odd reversed: if the preceding digit is odd, round up; otherwise round down. So, for example, 1.5 and 2.5 both round to 2.

By: Scott

Scott — Tue, 09 Nov 2004 17:20:03 +0000

Regarding the rounding of 0.5, I was also taught that it should round to 1. But what about 1.5? I would guess that Daniel was taught that it rounds to 2; I was taught that it also rounds to 1. I learned this in lab courses in undergraduate physics. The general rule was (is) that if the digit to the immediate left of the positition being rounded is even, round up; otherwise round down. The rationale is that otherwise, on average, you will end up
rounding up more often than down, skewing results slightly.

By: Joseph Scott's Blog

Joseph Scott's Blog — Tue, 09 Nov 2004 02:40:58 +0000

MySQL’s Funny Math
Daniel Lemire came across some funny math in MySQL. He ran ’select 11/5;’ and had MySQL give him 2.20, where PostgreSQL gave him 2. There is nothing wrong with MySQL’s answer, but it might throw off most programmers who be likely to expect the kin…