Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What is the average Tier when the postseason shows -, and the season is 2012–13?

### Inputs:
table_name: table, columns: ['Season', 'Tier', 'League', 'Postseason', 'European competitions']

### Response:
SELECT AVG Tier FROM table WHERE Postseason = – AND Season = 2012–13