SQL。每个用户的完整日期范围

使用Tally，它们在以下操作上确实非常快：

/*
Underwriter | UW_First   | UW_Last     |
------------------------------------------
Kim         | 11/1/2019  | 11/30/2019  |
Kim         | 12/1/2019  | 12/31/2019  |
Sarah       | 11/1/2019  | 11/30/2019  |
Sarah       | 12/1/2019  | 12/31/2019  |
Rebecca     | 11/1/2019  | 11/30/2019  |
*/
--Create sample table

CREATE TABLE dbo.YourTable (Underwriter varchar(10),
                            UW_First date,
                            UW_Last date);
GO

--Insert sample data    
INSERT INTO dbo.YourTable (Underwriter,UW_First,UW_Last)
SELECT RTRIM(U),
       CONVERT(date,F,101),
       CONVERT(date,L,101)
FROM (VALUES('Kim    ','11/1/2019','11/30/2019'),
            ('Kim    ','12/1/2019','12/31/2019'),
            ('Sarah  ','11/1/2019','11/30/2019'),
            ('Sarah  ','12/1/2019','12/31/2019'),
            ('Rebecca','11/1/2019','11/30/2019'))V(U, F, L);
GO

--Start creating the Tally    
WITH N AS(
    SELECT N
    FROM (VALUES(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL))N(N)),
--Create the tally, using Cross Joins.
Tally AS(
    SELECT TOP (SELECT MAX(DATEDIFF(DAY,UW_First,UW_Last))+1 FROM dbo.YourTable)
           ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) -1 AS I
    FROM N N1, N N2, N N3) --1000 days
--And then make the data set
SELECT YT.Underwriter,
       DATEADD(DAY,T.I,YT.UW_First) AS [Date]
FROM dbo.YourTable YT
     JOIN Tally T ON T.I <= DATEDIFF(DAY,YT.UW_First,YT.UW_Last)
ORDER BY YT.Underwriter,
         [Date];
GO

DROP TABLE dbo.YourTable;