user: Question: Which Date has a Runner(s)-up of Bernhard Langer, and a Tournament of AT&T Championship?
Columns: ['Date', 'Tournament', 'Winning score', 'Margin of victory', 'Runner(s)-up']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Oct 2, 2011', 'SAS Championship', '−11 (66-69-70=205)', '1 stroke', 'John Huston , Jeff Sluman']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Runner(s)-up" = 'Bernhard Langer' AND "Tournament" = 'AT&T Championship';