Android : Regex in SQLite query gives unrecognized token exception

I have the following query:

String selectQuery = "SELECT * FROM " + DOCUMENT_TABLE + " WHERE " + DOCUMENT_TYPE + " REGEXP " + "(^|,)(pdf)(,|$)";

At compile time I receive this error:

android.database.sqlite.SQLiteException: unrecognized token: "^" (code 1): , while compiling: SELECT * FROM DOCUMENTTABLE WHERE TYPE REGEXP (^|,)(pdf)(,|$)

The column from where clause has values written in the following format:

• doc,pdf


• pdf


• pdf,doc

How to use regex to retrieve the right information (my case, get all documents that are in pdf format, too)?