There is critical problem with filtering in sql table when there is JOIN in query. See screens. 

Query was generated with your Generate a query to the MySQL database.

Of course filtering starts to work when I disable Server Side Processing.

Please do something with that! And PLEASE don't send me this response: 

"if your MySQL-query based wpDataTable doesn’t work correctly 
with server-side processing, probably this is happening because
wpDataTables server has problems with parsing of the 
query and building new queries dynamically (happens rarely, but does 
sometimes). To avoid this please prepare a MySQL view (a stored query), 
which will return the data that you need, call it e.g. “view1” and then 
build a wpDataTabled based on a simple query like “SELECT * FROM view1″.

This is not enought. My query is simple like this:

SELECT wp_wpdatatable_3.`wdt_ID`,
       wp_wpdatatable_3.`time`,
       wp_users.`user_email`,
       wp_users.`user_nicename`,
       wp_users.`display_name`
FROM wp_wpdatatable_3
  INNER JOIN wp_users
     ON wp_wpdatatable_3.`userid` = wp_users.`ID`
WHERE 1=1 
   AND wp_wpdatatable_3.`groupid` = '5'

so if I want to filter this by email your PARSER only need to add AND to the and of the query!!!

...
AND wp_users.`user_email` = '[email protected]'

 You need to make it work. Only on our site we need to create 45! views to make it work. This is not possible! And for you this is really small effort. 

PS.

Search block don't work at all (it work only when SELECT select only fieldsfrom first table)

Column search fields seems to be working only for first table (from ex. wp_wpdatatable_3)

IF you show me, where in your files those filter queries are created then I will extend this functionality for tables with JOIN (only for JOIN for now) and I will return you results for everyone's benefit.