取消透视数据t-sql

CREATE TABLE Sales (
    ProductID INT,
    SaleDate DATE,
    Quantity INT
);

SELECT ProductID,
       [2021-Jan], [2021-Feb], [2021-Mar], ... -- 其他月份
FROM (
    SELECT ProductID, 
           DATEPART(YEAR, SaleDate) AS Year, 
           DATENAME(MONTH, SaleDate) AS Month, 
           Quantity
    FROM Sales
) AS SourceTable
PIVOT (
    SUM(Quantity)
    FOR Month IN ([2021-Jan], [2021-Feb], [2021-Mar], ...) -- 其他月份
) AS PivotTable;

SELECT ProductID, Year, Month, Quantity
FROM (
    SELECT ProductID,
           [2021-Jan], [2021-Feb], [2021-Mar], ... -- 其他月份
    FROM (
        SELECT ProductID, 
               DATEPART(YEAR, SaleDate) AS Year, 
               DATENAME(MONTH, SaleDate) AS Month, 
               Quantity
        FROM Sales
    ) AS SourceTable
    PIVOT (
        SUM(Quantity)
        FOR Month IN ([2021-Jan], [2021-Feb], [2021-Mar], ...) -- 其他月份
    ) AS PivotTable
) AS PivotedData
UNPIVOT (
    Quantity FOR Month IN ([2021-Jan], [2021-Feb], [2021-Mar], ...)
) AS UnpivotTable;