Table: match_data
Columns: date
opponents
h_a
result_f_a
attendance

Question: When did Manchester United play against Bristol City with an H/A of A?
SQL: SELECT "date" FROM match_data WHERE "h_a" = 'a' AND "opponents" = 'bristol city'

Question: How many people attended the match when Manchester United played against the Hearts?
SQL: SELECT SUM("attendance") FROM match_data WHERE "opponents" = 'hearts'