Question

I have three queries that get stats from the database, but the total does not add up correctly for my results. If I do the math myself this is what I get: // 440728 / 1128 = 390.72

However, the following is what is returned by my queries:

SELECT * FROM facebook_accts
         WHERE user_id IN (SELECT id FROM  `user_accts` WHERE owner_id = '121') 
// returns 1128

SELECT sum(friend_count) FROM facebook_accts
                         WHERE user_id IN
                            (SELECT id FROM  `user_accts` WHERE owner_id = '121') 
// returns 440728

SELECT avg(friend_count) FROM facebook_accts
                         WHERE user_id IN
                            (SELECT id FROM  `user_accts` WHERE owner_id = '121') 
// returns 392.11 (number formatted to two decimal places by php)

Answer 1

this may be happening because of column friend_count having some NULL values because SUM and AVG sunctions ignore NULL values. see here.