グループ結果の制限

Oracle SQL 入門

Hadrien Lacroix

Content Developer

例に戻る

SELECT Composer, AVG(Milliseconds)
FROM Track
WHERE UnitPrice = 0.99
GROUP BY Composer

| Composer        | AVG(Milliseconds) |
|-----------------|-------------------|
| Antonio Vivaldi | 199,086.0         |
| Pearl Jam       | 94,197.0          |
| Jimmy Page      | 474,888.3         |
| Carlos Santana  | 499,234.3         |
| ...             | ...               |

グループ化後の絞り込みは？

Oracle SQL 入門

WHERE の制約

  • WHERE はグループを絞れない
    • WHERE では集計関数は使えない
Oracle SQL 入門

WHERE の制約 例

SELECT Composer, AVG(Milliseconds)
FROM Track
GROUP BY Composer
WHERE AVG(Milliseconds) > 200000

syntax error at or near "WHERE"
LINE 4: WHERE AVG(Milliseconds) > 200000
        ^
Oracle SQL 入門

HAVING

SELECT Composer, AVG(Milliseconds)
FROM Track
GROUP BY Composer
HAVING AVG(Milliseconds) > 200000

| composer    | avg    |
|-------------|--------|
| George Duke | 274155 |
| Miles Davis | 391146 |
| R. Carless  | 251585 |
| ...         | ...    |
Oracle SQL 入門

HAVING でグループ結果を制限

HAVING 句の流れ

Oracle SQL 入門

HAVING

SELECT Composer, MAX(Milliseconds)
FROM Track
GROUP BY Composer
HAVING MAX(Milliseconds) > 200000

| composer    | max    |
|-------------|--------|
| George Duke | 274155 |
| Miles Davis | 907520 |
| R. Carless  | 251585 |
| ...         | ...    |
Oracle SQL 入門

別の例

SELECT Composer, SUM(UnitPrice)
FROM Track
WHERE GenreId = 1
GROUP BY Composer
HAVING COUNT(*) > 4

| composer      | sum  |
|---------------|------|
| AC/DC         | 7.92 |
| Chris Cornell | 9.90 |
| Eddie Vedder  | 8.91 |
| ...           | ...  |
Oracle SQL 入門

ガイドライン

  • SELECT と HAVING で異なる集計関数を使える

  • HAVING には必ず集計関数が入る

処理順序:

  1. 行を WHERE と GROUP BY で絞り込み
  2. グループに集計関数を適用
  3. HAVING でグループを絞り、出力
Oracle SQL 入門

Ayo berlatih!

Oracle SQL 入門

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