Is it possible to get SUM for total value of INTEGER values over many POSTS with WP_Query?

OK, I know not to directly query the database, but I need a total sum of all posts that have parent id X and I really don’t want to pull all the posts out and then loop over them to get the value I need. I just want to say something like

WP\_Query

\- return SUM of custom field rating value / TOTAL NUMBER OF POSTS
. where parent id = 1

Is this possible at all?

In the db I have

\- post id: 1. ratingValue: 5
\- post id: 2. ratingValue: 6
\- post id: 3. ratingValue: 1
\- post id: 4. ratingValue: 2

SUM would be 5+6+1+2=14
TOTAL NUMBER OF POSTS=4
14/4= 3.5

3.5 is the only value I want returned from my function.

TIA

 

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