Calculate the ratio of unemployed students who have never been absent from school.
ratio = CONCAT(DIVIDE(MULTIPLY(COUNT(unemployed.name WHERE month = 0), 100), COUNT(month)),'%'); unemployed students who have never been absent from school refers to (unemployed.name WHERE month = 0);
SELECT CAST(SUM(IIF(T2.month = 0, 1, 0)) AS REAL) * 100 / COUNT(T1.name) FROM unemployed AS T1 INNER JOIN longest_absense_from_school AS T2 ON T2.name = T1.name