Question: What is the percentage difference between month 0 absence and month 9 absence?
SQL: SELECT CAST(((SUM(IIF(month = 0, 1, 0)) - SUM(IIF(month = 9, 1, 0)))) AS REAL) * 100 / SUM(IIF(month = 0, 1, 0)) FROM longest_absense_from_school