CREATE TABLE table_7821 ("Goal" FLOAT, "Date" CLOB, "Venue" CLOB, "Score" CLOB, "Result" CLOB, "Competition" CLOB)

When was the venue mexico city, mexico with a goal of 8?
SELECT "Date" FROM table_7821 WHERE "Venue" = 'mexico city, mexico' AND "Goal" = '8'
SELECT "Date" FROM "table_7821" WHERE "Goal" = '8' AND "Venue" = 'mexico city, mexico'