Previous
data class Previous(val metric: String, val along: String, val shift: Int = 1, val period: AggregationDateUnit? = null) : DerivedExpression.Window
metric of the group shift steps earlier along the DATE_HISTOGRAM group along, every other group key equal: a step is one bucket of along, or one period (such as YEAR for the same period last year). The earlier groups are read over the query's own range of along's field, shifted. null when that group has no records.