What is the percentage of flights which landed at Pittsburgh were faster than scheduled?
percentage = MULTIPLY(DIVIDE(SUM(ACTUAL_ELAPSED_TIME < T2.CRS_ELAPSED_TIME), COUNT(Code)), 100); landed at refers to DEST; Pittsburgh refers to Description which contains 'Pittsburgh'; faster than scheduled refers to ACTUAL_ELAPSED_TIME < CRS_ELAPSED_TIME;
SELECT CAST(SUM(CASE WHEN T1.ACTUAL_ELAPSED_TIME < T1.CRS_ELAPSED_TIME THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(*) FROM Airlines AS T1 INNER JOIN Airports AS T2 ON T2.Code = T1.DEST WHERE T2.Description LIKE '%Pittsburgh%' AND T1.CRS_ELAPSED_TIME IS NOT NULL AND T1.ACTUAL_ELAPSED_TIME IS NOT NULL