Rlookup

relational-functions rlookup

syntax

  • rlookup(foreign_key, primary_key)

definition

rlookup(foreign_key, primary_key) results in a relation from the domain-unit of the foreign_key argument towards the domain unit of the primary key argument

applies to

  • foreign_key: an attribute which can serve as primary key for the domain unit of the primary_key argument, e.g. a region code.
  • primary_key: an attribute which can serve as primary key for it’s own domain unit and with the the same values-unit as the foreign_key attribute.

description

We advise that the second argument can be used as primary key for the domain unit of this argument.

If multiple instances of the second argument occur, the resulting value will be the first index-numbers found.

applies to

  • attributes foreign_key and primary_key with Numeric, Point, uint2, unit4, bool or string value-type

conditions

The values unit of the arguments foreign_key and primary_key must match.

example

attribute<Region> Region_rel (City) := rlookup(City/RegionCode, Region/RegionCode);
City/RegionCode Region_rel
100 0
200 1
300 2
200 1
400 3
null null
400 3

domain City, nr of rows = 7

Region/RegionCode
100
200
300
400
500

domain Region, nr of rows = 5