Database: cre_Doc_Template_Mgt
Question: What are the distinct template type descriptions for the templates ever used by any document?
SQL:
SELECT DISTINCT T1.template_type_description FROM Ref_template_types AS T1 JOIN Templates AS T2 ON T1.template_type_code  = T2.template_type_code JOIN Documents AS T3 ON T2.Template_ID  =  T3.template_ID