CREATE TABLE table_2771 ("Episode" CLOB, "Location" CLOB, "Headliner" CLOB, "Comedians" CLOB, "Airdate" CLOB)

What date did the show air when Sean Lock was the headliner?
SELECT "Airdate" FROM table_2771 WHERE "Headliner" = 'Sean Lock'
SELECT "Airdate" FROM "table_2771" WHERE "Headliner" = 'Sean Lock'