Based on all user compliments, find the percentage of low number of compliments on all compliments ID.
low number of compliments refers to number_of_compliments = 'Low'; percentage refers to DIVIDE(COUNT(number_of_compliments = 'Low'), COUNT(user_id)) * 100
SELECT CAST(SUM(CASE WHEN number_of_compliments = 'Low' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(user_id) FROM Users_compliments