Schema: CREATE TABLE table_name_50 (fa_cup INTEGER, total VARCHAR, fa_trophy VARCHAR, club VARCHAR)
Question: What is the sum of FA cups of club Stalybridge Celtic, which has more than 0 FA trophies and a total less than 20?
SQL: SELECT SUM(fa_cup) FROM table_name_50 WHERE fa_trophy > 0 AND club = "stalybridge celtic" AND total < 20