user: ### NOW ANSWER:
Question: What's the post position when the lengths behind is 0?
Columns: ['Finish Position', 'Lengths Behind', 'Post Position', 'Horse name', 'Trainer', 'Jockey', 'Owner', 'Post Time Odds']
Types: ['text', 'text', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1 st', '0', 7.0, 'Big Brown', 'Richard E. Dutrow, Jr.', 'Kent J. Desormeaux', 'IEAH Stables', '1-5 favorite']
SQL:

assistant: SELECT AVG("Post Position") FROM "Table" WHERE "Lengths Behind" = '0';