Join_equal_values
Relational functions join_equal_values
- join_equal_values(first_rel, second_rel)
join_equal_values(first_rel, second_rel) results in a new uint32 domain unit with entries for each combinations of all equal values of first_rel and second_rel. The functions results in three subitems:
- nr_1_rel: the index numbers of the combination of equal values in the domain unit of the first argument
- nr_2_rel: the index numbers of the combination of equal values in the domain unit of the second argument
- nr_X_rel: the equal value in the combination
The explicit: join_equal_values_uint64, join_equal_values_uint32,join_equal_values_uint16 and join_equal_values_uint8 functions can be used in the same manner as the join_equal_values function, to create a new domain unit with an explicit value type.
- first_rel: a uint32 relation
- second_rel: a uint32 relation
- The values unit of the arguments: first_rel and second_rel must match.
- The domain unit of arguments: first_rel and second_rel must be zero based.
- https://en.wikipedia.org/wiki/Pullback_(category_theory)
- https://www.w3schools.com/sql/sql_join_inner.asp
unit<uint32> RegionCity := join_equal_values(region/country_rel, city/country_rel);
| nr_1_rel | nr_2_rel | nr_X_rel |
|---|---|---|
| 0 | 1 | 0 |
| 1 | 1 | 0 |
| 2 | 0 | 1 |
| 3 | 0 | 1 |
| 4 | 2 | 2 |
domain CityRegionCombinations , nr of rows = 5
| region/country_rel |
|---|
| 0 |
| 0 |
| 1 |
| 1 |
| 2 |
domain region, nr of rows = 5
| city/country_rel |
|---|
| 1 |
| 0 |
| 2 |
domain city, nr of rows = 3
