Lookup

relational-functions lookup

syntax

  • lookup(relation, values)
  • values[relation]
  • relation -> values

definition

lookup(relation,values) or values[relation] or relation -> values results in a data-item with the values of the argument values for the domain-unit of the relation attribute.

The relation argument defines which values are looked up in the domain unit of the values attribute.

The resulting data item has the same values-unit as the values argument and the same domain unit as the relation argument.

applies to

  • relation: data-item with the index-numbers of the domain unit of the values attribute.
  • values: attribute with the requested values to be looked up.

description

The relation towards the domain unit of argument values can de derived from any foreign key attribute with the rlookup function.

The rjoin function can be used to relate on foreign key attributes, without the explicit use of index numbers.

example 

attribute<degrees> LTemp (City) := lookup(City/Region_rel, Region/Temp);
attribute<degrees> LTemp (City) := Region/Temp[City/Region_rel];
attribute<degrees> LTemp (City) := City/Region_rel -> Region/Temp;
City/Region_rel LTemp
0 12
1 11
2 null
1 11
3 14
null null
3 14

domain City, nr of rows = 7

Region/Temp
12
11
null
14
13

domain Region, nr of rows = 5

see also