STD_DEV_EACH ([MAX VALUES, ]GROUP, VALUE)
MAX VALUES:The maximum number of groups (Default: 2,147,483,647). Groups beyond this amount will be discarded. In some cases, depending on the data distribution, discarding groups via
MAX VALUESmay cause some data to be discarded from groups that would otherwise have been returned.
MAX VALUESis optional. If it is omitted there is, in effect, no limit.
GROUP:a field to sub-aggregate by
VALUE:a field in the sub-aggregation command