Subkueri di klausa FROM

Manipulasi Data di SQL

Mona Khalil

Data Scientist, Greenhouse Software

Subkueri di FROM

Restrukturisasi dan transformasi data Anda
- Ubah data dari long ke wide sebelum menyeleksi
- Prasaring data
Menghitung agregat dari agregat
- 3 tim mana yang memiliki rata-rata gol kandang tertinggi?
  1. Hitung AVG untuk tiap tim
  2. Ambil 3 nilai AVG tertinggi

Subkueri 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;

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

...ke kueri utama!


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)

...ke kueri utama!


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

...ke kueri utama!

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

...ke kueri utama!

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   |

Hal yang perlu diingat

Anda dapat membuat beberapa subkueri dalam satu FROM
- Beri alias!
- Gabungkan!
Anda dapat menggabungkan subkueri dengan tabel di FROM
- Sertakan kolom penggabung di keduanya!

Ayo berlatih!

Manipulasi Data di SQL