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