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

### Instruction:
What is the average opened year of Mini Estadi stadium in Barcelona, Spain?

### Inputs:
table_name: table, columns: ['Team', 'Stadium', 'Capacity', 'Opened', 'City']

### Response:
SELECT AVG Opened FROM table WHERE City = barcelona, spain AND Stadium = mini estadi