Join_equal_values
Relational functions join_equal_values
- join_equal_values(AtoX_rel, BtoX_rel)
join_equal_values(AtoX_rel, BtoX_rel) results in a uint32 domain unit that represents each combination of AtoX_rel and BtoX_rel that relate to the same X.. The function results in three subitems being attributes of this domain:
- first_rel (FKA nr_1_rel): the index numbers of each row in A that participates in a combination of rows that have the same X-values as rows in B.
- second_rel (FKA nr_2_rel): the index numbers of each row in B that participates in a combination of rows that have the same X-values as rows in A.
- X_rel (FKA 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.
- AtoX_rel: a uint32 relation
- BtoX_rel: a uint32 relation
- The values unit of the arguments: AtoX_rel and BtoX_rel must match and represent a valid domain X.
- The domain unit of arguments: AtoX_rel and BtoX_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);
| first_rel | second_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
