Hello Lina

Issues with sorting, filtering and search may occur with queries with JOINS, CONCATs and other functions

This is probably happening because wpDataTables server has problems with parsing of the query and building new queries dynamically (rarely happens, 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″.

Please note some this when working with the server-side processing feature:

• Please do not use “LIMIT” in the SELECT statement. wpDataTables adds it automatically and it will be overridden.
• Please do not use “ORDER BY” in the SELECT statement. wpDataTables has its own sorting engine so it makes no sense to use MySQL’s sorting, since it will be overridden. Also, server-side processing feature adds this part of statement automatically when users trigger the sorting on the front-end, and having it in initial statement may cause the table to crash.

Hello again Lina

You wouldn't see an SQL error, because there is none. 

The issue here is that wpDataTables server has problems with parsing of the query, and that is why search, sorting and filtering don't work.

The query is just fine, but having CONCAT, JOIN, UNION, and other types of similar statements can cause issues like this.

Please try creating a view, and the issue should be solved.