SUM of Aggregate functions
Ali Hirji Sep 16, 2016 8:01 AMHi all,
I'm relatively new to creating dashboards on Tableau (as it may become apparent with my question) and I'm in desperate need of some help. Firstly, just want to thank Shawn Wallwork for all his help so far  without him, I wouldn't be at the stage I am at the moment. Right, down to the question.
I am in the process of creating a table which holds information on call statistics by day. So, number of calls received (offered), number answered, answer rate, avg talk time, avg hold time, etc... My initial problem was converting time into a format that I was able to create calculations from. For example, a total of 00:02:00 (2 hours talk time) for 2 answered calls would equal an average of 00:01:00 (1 hour) talk time per call. With thanks and all credit to Shawn, *we* were able to break down the data to convert to seconds, divide that by whatever value to calculate the average (in seconds) and then convert it back into a suitable format hh:mm:ss.
My problem now lies when I want to create a calculated field off the back of what I have already calculated. Basically, to sum Avg Talk Time + Avg Hold Time + Avg Wrap Time (highlighted in the screen shot below) to equal the AHT (Average Handling Time). So my desired result is to have a column which sums these values and gives me the result of 11 minutes and 5 seconds (using the highlighted values in the screen shot below as an example). I've tried adding only the seconds to come up with the total seconds but because (i believe) i had to convert data source to seconds in the first place and then to a time format is what is making it fall over/error/fail. No matter what I try (I've also looked through this forum)  I keep getting this error "Argument to SUM (an aggregate function) is already an aggregation, and can not be further aggregated".
I was wondering whether anyone can help me solve this issues or if anyone has a fix for this. I must admit, I'm a little confused why it would be fine to do this on excel (i.e. sum together calculated cells) and not here on Tableau  unless I'm missing something? Any help would be very much appreciated. I have attached an extracted workbook should anyone what to see (or alternative, look at the formula Shawn created to convert date to seconds > time.). Any help would be very much welcomed!
Thank you in anticipation, Ali.

SampleDataTelephonyv4.twbx 3.2 MB