Come calcolare la pendenza in SQL

Il più pulito che potrei fare:

SELECT
    Scores.Date, Scores.Keyword, Scores.Score,
    (N * Sum_XY - Sum_X * Sum_Y)/(N * Sum_X2 - Sum_X * Sum_X) AS Slope
FROM Scores
INNER JOIN (
    SELECT
        Keyword,
        COUNT(*) AS N,
        SUM(CAST(Date as float)) AS Sum_X,
        SUM(CAST(Date as float) * CAST(Date as float)) AS Sum_X2,
        SUM(Score) AS Sum_Y,
        SUM(CAST(Date as float) * Score) AS Sum_XY
    FROM Scores
    GROUP BY Keyword
) G ON G.Keyword = Scores.Keyword;

Utilizza Simple Linear Regression per calcolare la pendenza.

Risultato:

Date         Keyword        Score         Slope
2012-01-22   water bottle   0,010885442   0,000334784345222076
2012-01-23   water bottle   0,011203949   0,000334784345222076
2012-01-24   water bottle   0,008460835   0,000334784345222076
2012-01-25   water bottle   0,010363991   0,000334784345222076
2012-01-26   water bottle   0,011800716   0,000334784345222076
2012-01-27   water bottle   0,012948411   0,000334784345222076
2012-01-28   water bottle   0,012732459   0,000334784345222076
2012-01-29   water bottle   0,011682568   0,000334784345222076

Ogni sistema di database sembra avere un approccio diverso per convertire le date in numeri:

• MySQL: TO_SECONDS(date) o TO_DAYS(date)
• Oracolo: TO_NUMBER(TO_CHAR(date, 'J')) o date - TO_DATE('1','yyyy')
• MS SQL Server: CAST(date AS float) (o equivalente CONVERT )