Lookup
Relational functions lookup
lookup(relation,values) or values[relation] 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.
- 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.
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.
attribute<degrees> LTemp (City) := lookup(City/Region_rel, Region/Temp); attribute<degrees> LTemp (City) := Region/Temp[City/Region_rel];
| 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
