mysql - Subquery or INNER JOIN? -

I have 3 tables that represent emails like attachments, accordingly, there are zero, one or more attachments in the email .

Three tables email , attachments and files .

Email - Each email is mentioned in an email and has a message id

attachment - each line There can be a message ID and a file ID with multiple lines with the same message ID.

files - Each file is referenced in a file and it has fileID and file size (size) in it

I get a result in mysql I am trying to list the email ID and the total size of all the files and no success. I files using SUM (size) and a INNER JOIN I can get a total size, but I do not have an e-mail ID and a list of total file size Can writing.

Should it use multiple INNER JOIN S? INNER JOIN and a subquery? And then a group B ? Subquery and then a IN even one direction would be really useful.

Manipulation in PHP seems ridiculously expensive.

Many thanks!