lib/dataset/actions.js
function (column, cb) {
            return this.__aggregateDataset().get(sql.max(column).minus(sql.min(column)), cb);
        }
function (column, cb) {
            return this.__aggregateDataset().get(sql.max(column).minus(sql.min(column)), cb);
        }
function ( column , cb ) { return this . __aggregateDataset ( ) . get ( sql . max ( column ) . minus ( sql . min ( column ) ) , cb ) ; }
Returns a promise that is resolved with the interval between minimum and maximum values
for the given column.

@example
// SELECT (max(id) - min(id)) FROM table LIMIT 1
DB.from("table").interval("id").chain(function(interval){
//(e.g) interval === 6
});

@param {String|patio.sql.Identifier} column to find the interval of.
@param {Function} [cb] a function to be called when the aciton is complete

@return {comb.Promise} a promise that will be resolved with the interval between the min and max values
of the column.
Returns a promise that is resolved with the interval between minimum and maximum values for the given column .