anchor.diff:        max(a_f),
         avg(a_i),
         avg(a_f),
  +      per(a_f, 50),
  +      per(a_f, 75),
         count(*))
   ----
   
  
positive.code: * `overfetch`: (Default 150) Over-fetching is used to provide accurate aggregations over high cardinality fields.
  * `method`: The JSON facet API aggregation method.
  * `bucketSizeLimit`: Sets the absolute number of rows to fetch. This is incompatible with rows, offset and overfetch. This value is applied to each dimension. '-1' will fetch all the buckets.
  * `metrics`: List of metrics to compute for the buckets. Currently supported metrics are `sum(col)`, `avg(col)`, `min(col)`, `max(col)`, `count(*)`.
  
  === facet Syntax
  
  
negative.code: 
  * `collection`: (Mandatory) Collection the stats will be aggregated from.
  * `q`: (Mandatory) The query to build the aggregations from.
  * `metrics`: (Mandatory) The metrics to include in the result tuple. Current supported metrics are `sum(col)`, `avg(col)`, `min(col)`, `max(col)`, `count(*)`,  `per(col, 50)`. The `per` metric calculates a percentile
  for a numeric column and can be specified multiple times in the same stats function.
  
  
  === stats Syntax
  
  