MySQL Werid Results

MySQL Werid Results

Ok...
Why on earth should this be happening? I have over a million rows in a
table that records temperature data on my homebrewing activity.
create table temperature (
notes varchar(50)
,temperature decimal(4,1)
,temperature1 decimal(4,1)
,temperature2 decimal(4,1)
) ;
In my notes column, I accidently executed the following:
update temperature set notes = 'xyz' where notes = 'xyz123' ;
When I meant to execute the following:
update temperature set notes = 'x' where notes = 'xyz123' ;
Ok, no problem, I will simply set notes to x where notes = xyz ...
update temperature set notes = 'x' where notes = 'xyz' ;
commit ;
Ok, there should be 0 results for the following:
select count(*) from temperature where notes = 'zyx';
NO: THIS DOESN'T NECESSARILY RETURN 0 !!!!!!!!!
I can execute the previous update and commit as many times as I want. It
doesn't matter. The select count(*) returns the same thing.
I am familiar with Oracle and this is just absurd to me. What possible
reason could exist for an update statement to not update all records
according to the WHERE clause?