CREATE TABLE table_204_11 (id DECIMAL, "year" DECIMAL, "fbs opponent" TEXT, "result" TEXT, "opponent's conference" TEXT, "opponent's head coach" TEXT, "charleston southern's head coach" TEXT)

who was the longest head coach ?
SELECT "charleston southern's head coach" FROM table_204_11 GROUP BY "charleston southern's head coach" ORDER BY COUNT(*) DESC LIMIT 1
SELECT "charleston southern's head coach" FROM "table_204_11" GROUP BY "charleston southern's head coach" ORDER BY COUNT(*) DESC NULLS LAST LIMIT 1