Collecting two separate column results from mySQL query - php

Question

I have two database tables containing similar data - one is the amount of work completed by a process, the other is the amount of errors made by that process.
I would like to display the percentage of right first time work.
My query for counting the number of items by process is:
SELECT Counter.Process, count( Counter.Process ) AS count
FROM Counter WHERE (TIME BETWEEN '2012-07-01 00:00:00' AND '2012-07-06 23:59:59')
GROUP BY Counter.Process
ORDER BY count DESC
The above gives me a list similar to:
Process | count
-------------------
Process A | 40
Process B | 32
Process C | 102
Process D | 23
I have a second table with the same fields in it for recording errors, called 'Errors'.
By using the same query (but changing the table names obviously) I can get a list of processes and errors.
What I want to do is create a PHP web page showing the percentage of errors per process.
My problem is if I create the two queries separately, when I loop through them using a PHP Where loop I don't know how to make the calculation to show the percentage.
I tried using a UNION between the two SQL queries, but I can't get it to show the two different count readings against the process.
Ideally, I'd like a way to show the data like this:
Process | Counter.count | Errors.count
Process A 40 2
Process B 32 0
Process C 102 18
Process D 23 8
I would really appreciate any advice/suggestions as to how I can accomplish this - if you need more info on my database tables, please let me know
Thanks for reading
S

Answer 1

I did not run it so there might be mistakes. you can make the two selects, and left join the results:
select s.process, s.success_count, e.error_count
from
(SELECT Counter.Process as process, count( Counter.Process ) AS success_count
FROM Counter
WHERE (TIME BETWEEN '2012-07-01 00:00:00' AND '2012-07-06 23:59:59')
GROUP BY Counter.Process
) s left join
(SELECT Errors.Process, count( Errors.Process ) AS error_count
FROM Errors
WHERE (TIME BETWEEN '2012-07-01 00:00:00' AND '2012-07-06 23:59:59')
GROUP BY Errors.Process
) e
on (s.Process = e.process)

Answer 2

I personally prefer to run situations like this through PHP as it confuses me less, so I will explain how I think I would do it in PHP (I say 'think' because I might not know something about your database structure or system specifications that would make me thing otherwise):
$rows = array();
$res = mysql_query('SELECT Counter.Process, count( Counter.Process ) AS count
FROM Counter WHERE (TIME BETWEEN '2012-07-01 00:00:00' AND '2012-07-06 23:59:59')
GROUP BY Counter.Process
ORDER BY count DESC');
while ($arr = mysql_fetch_assoc($res))
{
$rows[] = $arr;
}
$res2 = mysql_query('SELECT Errors.Process, count( Errors.Process ) AS count
FROM Counter WHERE (TIME BETWEEN '2012-07-01 00:00:00' AND '2012-07-06 23:59:59')
GROUP BY Errors.Process
ORDER BY count DESC');
while ($arr2 = mysql_fetch_assoc($res2)
{
for ($i=0; $i<count($rows); $i++)
{
if ($arr2["Process"] == $data[$i]["process"])
{
break;
}
//Do your functions with $arr and $data[$i] at this point...
}
}

Answer 3

Doing it without a subquery should be simple:
SELECT
Counter.Process
, COUNT(Counter.Process) AS ProcessCount
, COUNT(Errors.Process) AS ProcessErrors
FROM
Counter
LEFT JOIN
Errors
ON Counter.Process = Errors.Process
WHERE
Counter.TIME BETWEEN '2012-07-01 00:00:00' AND '2012-07-06 23:59:59'
GROUP BY
Counter.Process
You can do an explain on both queries to see which is the best for your data.
-edit: I've changed it to a LEFT JOIN so you don't miss rows if a process has no errors.

Answer 4

You could use a sub-query:
SELECT Counter.Process, count( Counter.Process ) AS Count,
(SELECT count(Errors.Process)
FROM Errors
WHERE Process=Counter.Process
AND (TIME BETWEEN '2012-07-01 00:00:00' AND '2012-07-06 23:59:59')) AS Errors
FROM Counter WHERE (TIME BETWEEN '2012-07-01 00:00:00' AND '2012-07-06 23:59:59')
GROUP BY Counter.Process
ORDER BY count DESC
Regards,
Neil.