What are the code and description of the least frequent detention type ?
SELECT T1.detention_type_code ,  T2.detention_type_description FROM Detention AS T1 JOIN Ref_Detention_Type AS T2 ON T1.detention_type_code  =  T2.detention_type_code GROUP BY T1.detention_type_code ORDER BY count(*) ASC LIMIT 1
least frequent detention type refers to MIN(COUNT(detention_type_code)); code and description of detention type involves joining tables on detention_type_code;