Database: chicago_crime
Question: What is the percentage of crime cases that have been classified as "drug abuse" by the FBI and happened on the street?
SQL: SELECT CAST(SUM(CASE WHEN T2.title = 'Drug Abuse' AND T1.location_description = 'STREET' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.fbi_code_no) FROM Crime AS T1 INNER JOIN FBI_Code AS T2 ON T1.fbi_code_no = T2.fbi_code_no