FROM ifadesinde alt sorgular

SQL ile Veri İşleme

Mona Khalil

Data Scientist, Greenhouse Software

FROM içinde alt sorgular

Verinizi yeniden yapılandırın ve dönüştürün
- Seçmeden önce veriyi uzun formdan geniş forma dönüştürme
- Ön filtreleme
Toplamların toplamını hesaplama
- En yüksek ev sahibi gol ortalamasına sahip 3 takım hangisi?
  1. Her takım için AVG hesaplayın
  2. AVG değerlerinin en yüksek 3’ünü alın

FROM alt sorguları...

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 |

...ana sorgulara!


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)

...ana sorgulara!


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

...ana sorgulara!

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

...ana sorgulara!

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   |

Unutulmaması gerekenler

Tek bir FROM ifadesinde birden çok alt sorgu oluşturabilirsiniz
- Bunlara takma ad verin!
- Birleştirin!
FROM içinde bir alt sorguyu bir tabloyla birleştirebilirsiniz
- Her iki tabloda da birleştirme sütunlarını ekleyin!

Haydi pratik yapalım!

SQL ile Veri İşleme