Quantile digest functions#
Data structures#
A quantile digest is a data sketch which stores approximate percentile
information. The Trino type for this data structure is called qdigest
,
and it takes a parameter which must be one of bigint
, double
or
real
which represent the set of numbers that may be ingested by the
qdigest
. They may be merged without losing precision, and for storage
and retrieval they may be cast to/from VARBINARY
.
Functions#
- merge(qdigest) qdigest
Merges all input
qdigest
s into a singleqdigest
.
- value_at_quantile(qdigest(T), quantile) T #
Returns the approximate percentile value from the quantile digest given the number
quantile
between 0 and 1.
- values_at_quantiles(qdigest(T), quantiles) -> array(T)#
Returns the approximate percentile values as an array given the input quantile digest and array of values between 0 and 1 which represent the quantiles to return.
- qdigest_agg(x) -> qdigest([same as x])#
Returns the
qdigest
which is composed of all input values ofx
.
- qdigest_agg(x, w) -> qdigest([same as x])
Returns the
qdigest
which is composed of all input values ofx
using the per-item weightw
.
- qdigest_agg(x, w, accuracy) -> qdigest([same as x])
Returns the
qdigest
which is composed of all input values ofx
using the per-item weightw
and maximum error ofaccuracy
.accuracy
must be a value greater than zero and less than one, and it must be constant for all input rows.