In drug abuse crimes, what percentage is related to cannabis?
drug abuse crime refer to title = 'Drug Abuse'; percentage = Divide (Count (secondary_description LIKE '%CANNABIS%'), Count (secondary_description)) * 100
SELECT CAST(COUNT(CASE WHEN T1.secondary_description LIKE '%CANNABIS%' THEN T1.secondary_description END) AS REAL) * 100 / COUNT(T1.secondary_description) FROM IUCR AS T1 INNER JOIN Crime AS T2 ON T2.iucr_no = T1.iucr_no INNER JOIN FBI_Code AS T3 ON T3.fbi_code_no = T2.fbi_code_no WHERE T3.title = 'Drug Abuse'