Self joins

SQL में डेटा जॉइन करना

Maham Faisal Khan

Senior Content Developer, DataCamp

Self joins

Self joins वे टेबल हैं जो खुद से ही जोड़े जाते हैं
इन्हें एक ही टेबल के हिस्सों की तुलना करने के लिए इस्तेमाल किया जा सकता है

world leaders डेटाबेस की prime_ministers टेबल

world leaders डेटाबेस की prime_ministers टेबल, जिसमें तीन कॉलम हैं: country, continent और prime_minister.

Prime minister, meet prime minister

SELECT 
    p1.country AS country1, 
    p2.country AS country2, 
    p1.continent
FROM prime_ministers AS p1
INNER JOIN prime_ministers AS p2

ON p1.continent = p2.continent
LIMIT 10;

Prime minister, meet prime minister

| country1   | country2   | continent     |
|------------|------------|---------------|
| Egypt      | Egypt      | Africa        |
| Portugal   | Spain      | Europe        |
| Portugal   | Norway     | Europe        |
| Portugal   | Portugal   | Europe        |
| Vietnam    | Oman       | Asia          |
| Vietnam    | Brunei     | Asia          |
| Vietnam    | India      | Asia          |
| Vietnam    | Vietnam    | Asia          |
| Haiti      | Haiti      | North America |
| India      | Oman       | Asia          |
| India      | Brunei     | Asia          |

Prime minister, meet prime minister

SELECT 
    p1.country AS country1, 
    p2.country AS country2, 
    p1.continent
FROM prime_ministers AS p1
INNER JOIN prime_ministers AS p2
ON p1.continent = p2.continent 

    AND p1.country <> p2.country;

Self join किया हुआ prime_ministers टेबल

|------------|------------|-------------|
| country1   | country2   | continent   |
|------------|------------|-------------|
| Portugal   | Spain      | Europe      |
| Portugal   | Norway     | Europe      |
| Vietnam    | Oman       | Asia        |
| Vietnam    | Brunei     | Asia        |
| Vietnam    | India      | Asia        |
| India      | Oman       | Asia        |
| India      | Brunei     | Asia        |
| India      | Vietnam    | Asia        |
| Norway     | Spain      | Europe      |
| Norway     | Portugal   | Europe      |
|------------|------------|-------------|

अभ्यास करते हैं!

SQL में डेटा जॉइन करना