user: Question: What is the average Tier when the postseason shows -, and the season is 2012–13?
Columns: ['Season', 'Tier', 'League', 'Postseason', 'European competitions']
Types: ['text', 'real', 'text', 'text', 'text']
Sample row: ['1997–98', 2.0, '2. BBL', '–', '–']
SQL:

assistant: SELECT AVG("Tier") FROM "Table" WHERE "Postseason" = '–' AND "Season" = '2012–13';