{
  "columns": ["sum(invoiceAmount) as amount", "count(invoiceId) as bills", "averageAmount"],
  "calculatedFields": [{"name": "averageAmount", "expression": "sum(invoiceAmount) / nullif(count(invoiceId), 0)"}],
  "slice": [{"field": "invoiceDate", "op": "[)", "value": ["2012-01-01", "2013-01-01"]}],
  "limit": 1
}