sql - 如何在SQL函数中计算不同的趋势线类型

Question

我一直在寻找一种计算 Excel 的好方法，例如桌面应用程序仪表板图表的趋势线。

最常见的趋势类型一定是这样的

Type = 1 Linear Y = a + b*X
Type = 2 EXponential Y = a*e^(b*X)   
Type = 3 Logarithmic Y = a + b*ln(X)
Type = 4 Power Y = a*X^b

这就是我解决问题的方法。

Answer 1

正如我在其他评论中提到的，这可以写成内联 TVF，而不是多行 TVF。我从字面上理解了 OP 的解决方案，但是，一些 CTE 允许我们做到这一点:

CREATE FUNCTION dbo.tvf_TrendLine (@Type tinyint,
                                   @Rawdata XYTableType READONLY)
RETURNS TABLE
AS RETURN
    WITH xy AS(
    SELECT CONVERT(decimal(38,10),COUNT(*)) AS n,
           CONVERT(decimal(38,10),SUM(CASE WHEN @Type IN (3,4) THEN LOG(X) ELSE X END)) AS x,
           CONVERT(decimal(38,10),SUM(CASE WHEN @Type IN (3,4) THEN LOG(X) * LOG(X) ELSE X * X END)) AS x2,
           CONVERT(decimal(38,10),SUM(CASE WHEN @Type IN (2,4) THEN LOG(Y) ELSE Y END)) AS y,
           CONVERT(decimal(38,10),SUM(CASE WHEN @Type IN (2,4) THEN LOG(Y) * Y ELSE Y * Y END)) AS y2,
           CONVERT(decimal(38,10),SUM(CASE WHEN @Type = 2 THEN X * LOG(Y) WHEN @Type = 3 THEN LOG(X) * Y WHEN @Type = 4 THEN LOG(X) * LOG(Y) ELSE X * Y END)) AS xy
        FROM @RawData
        WHERE Y IS NOT NULL),
    ab AS(
        SELECT n,
               x,
               x2,
               y,
               Y2,
               xy,
               CONVERT(decimal(38,10),CASE WHEN @Type IN (2,4) THEN EXP((x2 * y - x * xy) / (n * x2 - x * x))
                                           ELSE (x2 * y - x * xy) / (n * x2 - x * x)
               END) AS a,
               CONVERT(decimal(38,10),(n * xy - x * y) / (n * x2 - x * x)) AS b
        FROM xy)
    SELECT rd.X,
           rd.Y,
           CASE
                WHEN @Type = 2 THEN ab.a * EXP(LOG(EXP(1)) * (ab.b * rd.X))
                WHEN @Type = 3 THEN ab.a + ab.b * LOG(rd.X)
                WHEN @Type = 4 THEN ab.a * EXP(LOG(rd.X) * ab.b)
                ELSE ab.a + ab.b * rd.X
           END AS Yt
    FROM @Rawdata rd
         CROSS JOIN ab;
GO

这返回的结果与OP的答案完全相同。