Teiid translators can expose a procedure to execute arbitrary source queries. When operating with a dynamic vdb the appropriate metadata is automatically made available to the engine, but in Designer the user must manually add a procedure definition. For many users this is a difficult process - see the forum link.
The complications here are that the procedure is selectively enabled and is allowed to have different names based upon the translator properties.
The general procedure form is:
create foreign procedure native (query in string, params in object varidaic) returns table(row_value object)