Question

My webserver is running MySQL client version 5.1.56.

My devserver is running MySQL client version 5.0.7.

This query gives me the same result on both servers:

SELECT scenario_user_ratings.userid,
       AVG(scenario_user_ratings.rating)
FROM scenario_user_ratings
GROUP BY scenario_user_ratings.userid

both report result:

userid  AVG(scenario_user_ratings.rating)
1       3.3659
21      2.8000
22      3.2069

but this query yields different results

SELECT * FROM ( SELECT scenario_user_ratings.userid,
                       AVG(scenario_user_ratings.rating)
                FROM scenario_user_ratings
                GROUP BY scenario_user_ratings.userid) tabl 
WHERE tabl.userid < 5

Dev MySQL v5.0.7 result

userid  AVG(scenario_user_ratings.rating)
1       0.9999  <-- average values are always this, regardless

Web MySQL v5.1.56 result

userid  AVG(scenario_user_ratings.rating)
1       3.3659  <-- correct

Apart from the obvious comment of dev environment should always match production can someone please explain to me how putting the original query into another query is nuking my AVG() values to 0.99999 ? I’ve narrowed it down to that particular action, and only for this local version of MySQL.

Thank you.

Answer 1

see here

if you encounter the same problem, you can simply replace the AVG function by the combination SUM/COUNT.
For example, the following query:

SELECT student_name, AVG(test_score)
FROM student
GROUP BY student_name;
can be replaced by the one below:

SELECT student_name, SUM(test_score)/COUNT(test_score)
FROM student
GROUP BY student_name;