Count

Aggregation functions count

syntax

  • count(a)
  • count(a, relation)

definition

  • count(a) results in an uint32 parameter with the number of non Null values of Attribute a.
  • count(a, relation) results in an uint32 attribute with the number of non null values of attribute a, grouped by relation. The Domain unit of the resulting attribute is the Values unit of the relation.

applies to

  • attribute a with Numeric or Point value type
  • relation with value type of the group CanBeDomainUnit

conditions

The domain unit of arguments a and relation must match.

performance

  • Without relation: O(n) where n = number of elements in the domain of a. Single pass counting non-null values.
  • With relation: O(n) where n = number of elements in the domain of a. Counts non-null values per group during a single pass.

example 

1. parameter<uint32> countNrInh                := count(City/NrInhabitants); result = 6
2. attribute<uint32> countNrInhRegion (Region) := count(City/NrInhabitants, City/Region_rel);
City/NrInhabitants City/Region_rel
550 0
525 1
300 2
500 1
200 3
175 null
null 3

domain City, nr of rows = 7

countNrInhRegion
1
2
1
1
0

domain Region, nr of rows = 5

see also