sql查询和php脚本显示每日平均问题

Question

In my questions table, each post is timestamped (MM-DD-YYYY). Each individual post has a QuestionID, and a response has both a QuestionID and ResponseID. I want to run a php script that will grab all questions (all posts where ResponseID = null) and display how many questions per day.

I'd like it to be avg questions per day since June 1, 2010.

Your help is much appreciated. Thank you!

Answer 1

This gets each day, and the number of questions:

select q.myTimestamp, count(*) 
from questionsTable q 
where q.myTimeStamp >= '6/1/2010'
and q.ResponseID IS NULL
group by myTimestamp

To get the average you need both the count of days, and sum of number of questions... I would probably do this with 2 queries to MySQL and calculate in PHP.

$query1 = "select count(*) as totalCount from questionsTable where myTimestamp >= '6/1/2010' and ResponseID IS NULL";
$query2 = "select count(*) as totalDays from (select distinct myTimestamp from questionsTable where myTimestamp >= '6/1/2010' and ResponseID IS NULL) a";

$res1 = mysql_query($query1);
$res2 = mysql_query($query2);

$row1 = mysql_fetch_array($res1);
$row2 = mysql_fetch_array($res2);

$avgPostCount = ($row1['totalCount'] / $row2['totalDays']);

not optimal, but should work..

I made an assumption, that you wouldn't want to count days where there were no questions.. otherwise it could be simplified to one query using a mysql function to get the number of days since 6/1/2010.

Answer 2

SELECT
    AVG(NumQuestions)
FROM
    (
        SELECT
            COUNT(*) AS NumQuestions
        FROM
            Questions
        WHERE
            ResponseID IS NULL AND
            Question_Date >= '2010-06-01'
        GROUP BY
            Question_Date
    ) AS MySubquery

On second thought: This is silly. If you want to know the average number of questions per day since a given day, you may as well just count the number of questions (simple) and then divide by the number of days that have elapsed since then. Also, the above query gives inaccurate results if there are days on which nobody asked a question.