RedshiftでのCTEの活用

Redshift入門

Jason Myers

Principal Architect

共通テーブル式（CTE）

一時的な結果セット
クエリを簡潔にする
サブクエリの代替

サブクエリとCTEの構造

SELECT division_name,
       revenue_total
       -- Subquery for top 10 divions by revenue
  FROM (SELECT division_id,
               SUM(revenue) AS revenue_total
          FROM orders
         GROUP BY division_id
         ORDER BY revenue_total DESC
         LIMIT 10) top_ten_divisions_by_rev
 WHERE revenue_total > 100000;

-- CTE for top 10 divions by revenue
WITH top_ten_divisions_by_rev AS (
  SELECT division_id,
         SUM(revenue) AS revenue_total
    FROM orders
   GROUP BY division_id
   ORDER BY revenue_total DESC
   LIMIT 10)


-- Main query
SELECT division_id,
       revenue_total
       -- FROM our CTE
  FROM top_ten_divisions_by_rev
 WHERE revenue_total > 100000;

複数のCTE

-- Top 10 divisions by revenue CTE
WITH top_ten_divisions_by_rev AS(
  SELECT division_id,
         SUM(revenue) AS revenue_total
    FROM orders
   GROUP BY division_id
   ORDER BY revenue_total DESC
   LIMIT 10),

-- Division ID and Name CTE
division_names AS(
  SELECT id AS division_id,
         name AS division_name
    FROM divisions)

-- Main query
SELECT division_name,
       revenue_total
       -- FROM Top 10 CTE
  FROM top_ten_divisions_by_rev
  -- Joining so we can use the division name
  JOIN division_names USING (DIVISION_ID)
 WHERE revenue_total > 100000;

複数CTEとCTEの結合

-- Selecting the division names
WITH division_names AS(
  SELECT id AS division_id,
         name AS division_name
    FROM divisions),
-- Selecting the top ten divisions by revenue
top_ten_divisions_by_rev AS(
  SELECT division_name,
         SUM(revenue) AS revenue_total
    FROM orders
    -- Joining in the division_names CTE
    JOIN divisions USING (division_id)
   GROUP BY division_name
   ORDER BY revenue_total DESC
   LIMIT 10);

カーニハンの法則

デバッグは最初にプログラムを書くより2倍難しい。だから、書くときに出せる限りの巧妙さを尽くすなら、どうやってデバッグするつもりだい？

CTEのパフォーマンス

サブクエリと同等
再利用するならサブクエリより有利

SQLコードと実行順序

Passons à la pratique !

Redshift入門