FROM स्टेटमेंट में सबक्वेरीज़

SQL में Data Manipulation

Mona Khalil

Data Scientist, Greenhouse Software

FROM में सबक्वेरीज़

अपने डेटा को पुनर्संरचित और ट्रांसफॉर्म करें
- चुनने से पहले long से wide में ट्रांसफॉर्म करें
- पहले से प्री-फिल्टर करें
aggregates के ऊपर aggregates निकालें
- "किस 3 टीमों के home goals का औसत सबसे अधिक है?"
  1. हर टीम के लिए AVG निकालें
  2. AVG के टॉप 3 मान लें

FROM सबक्वेरीज़...

SELECT
  t.team_long_name AS team,
  AVG(m.home_goal) AS home_avg
FROM match AS m
LEFT JOIN team AS t
ON m.hometeam_id = t.team_api_id
WHERE season = '2011/2012'
GROUP BY team;

| team                 | home_avg         |
|----------------------|------------------|
| 1. FC Köln           | 1.13725490196078 |
| 1. FC Nürnberg       | 1.27058823529412 |
| 1. FSV Mainz 05      | 1.43697478991597 |
| AC Ajaccio           | 1.12280701754386 |

...मुख्य क्वेरी तक!


FROM (SELECT
          t.team_long_name AS team,
          AVG(m.home_goal) AS home_avg
      FROM match AS m
      LEFT JOIN team AS t
      ON m.hometeam_id = t.team_api_id
      WHERE season = '2011/2012'
      GROUP BY team)

...मुख्य क्वेरी तक!


FROM (SELECT
          t.team_long_name AS team,
          AVG(m.home_goal) AS home_avg
      FROM match AS m
      LEFT JOIN team AS t
      ON m.hometeam_id = t.team_api_id
      WHERE season = '2011/2012'
      GROUP BY team) AS subquery

...मुख्य क्वेरी तक!

SELECT team, home_avg
FROM (SELECT
          t.team_long_name AS team,
          AVG(m.home_goal) AS home_avg
      FROM match AS m
      LEFT JOIN team AS t
      ON m.hometeam_id = t.team_api_id
      WHERE season = '2011/2012'
      GROUP BY team) AS subquery

...मुख्य क्वेरी तक!

SELECT team, home_avg
FROM (SELECT
          t.team_long_name AS team,
          AVG(m.home_goal) AS home_avg
      FROM match AS m
      LEFT JOIN team AS t
      ON m.hometeam_id = t.team_api_id
      WHERE season = '2011/2012'
      GROUP BY team) AS subquery
ORDER BY home_avg DESC
LIMIT 3;

| team           | home_avg |
|----------------|----------|
| FC Barcelona   | 3.8421   |
| Real Madrid CF | 3.6842   |
| PSV            | 3.3529   |

याद रखने योग्य बातें

आप एक ही FROM स्टेटमेंट में कई सबक्वेरीज़ बना सकते हैं
- उन्हें alias दें!
- उन्हें join करें!
आप FROM में किसी टेबल से सबक्वेरी join कर सकते हैं
- दोनों टेबल में joining कॉलम रखें!

अभ्यास करते हैं!

SQL में Data Manipulation