Uhusiano Maradufu na Jedwali Moja katika PHP
Wacha tuwe na miji:
| id | name |
|---|---|
| 1 | city1 |
| 2 | city2 |
| 3 | city3 |
Wacha tuwe na njia kati ya miji, wakati kila njia ina mwanzo wa mji na mwisho wa mji:
| id | name | from_city_id | to_city_id |
|---|---|---|---|
| 1 | route1 | 1 | 2 |
| 2 | route2 | 2 | 3 |
Wacha tuseme tunataka kupata njia pamoja na miji. Ugumu hapa unawakilishwa na ukweli kwamba kila njia ina miji miwili: mwanzo na mwisho.
Inabadilika kuwa jedwali la miji linahitaji kujiunga mara mbili. Kwa kila muunganisho jedwali italazimika kubadilisha jina:
SELECT
from_cities.name as from_city_name,
to_cities.name as to_city_name
FROM
routes
LEFT JOIN cities as from_cities
ON from_cities.id=routes.from_city_id
LEFT JOIN cities as to_cities
ON to_cities.id=routes.to_city_id
Wacha tuwe na watumiaji. Kwa kila mtumiaji ana baba na mama. Andika muundo wa uhifadhi.
