user: Question: What date did the show air when Sean Lock was the headliner?
Columns: ['Episode', 'Location', 'Headliner', 'Comedians', 'Airdate']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['1x01', 'Edinburgh Playhouse', 'Rhod Gilbert', 'Kevin Bridges Stewart Francis Mark Watson', '6 June 2009']
SQL:

assistant: SELECT "Airdate" FROM "Table" WHERE "Headliner" = 'Sean Lock';