SQL Server 2019

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DECLARE @__dateRange_StartDate_4 DATETIME ='2021-03-01T00:00:00.000'
DECLARE @__dateRange_EndDate_3 DATETIME ='2021-03-31T23:59:59.999'

SELECT DATEDIFF(DAY, '2021-03-01T00:00:00.000', '2021-03-31T23:59:59.999') + 1

SELECT DATEDIFF(DAY, @__dateRange_StartDate_4, @__dateRange_EndDate_3) + 1

SELECT @__dateRange_EndDate_3

(No column name)

31

(No column name)

32

(No column name)

2021-04-01 00:00:00.000

DECLARE @__dateRange_StartDate_4 DATETIME2 ='2021-03-01T00:00:00.000'
DECLARE @__dateRange_EndDate_3 DATETIME2 ='2021-03-31T23:59:59.999'

SELECT DATEDIFF(DAY, '2021-03-01T00:00:00.000', '2021-03-31T23:59:59.999') + 1

SELECT DATEDIFF(DAY, @__dateRange_StartDate_4, @__dateRange_EndDate_3) + 1

SELECT @__dateRange_EndDate_3

(No column name)

31

(No column name)

31

(No column name)

2021-03-31 23:59:59

DECLARE @__dateRange_StartDate_4 DATETIME ='2021-03-01T00:00:00.000'
DECLARE @__dateRange_EndDate_3 DATETIME ='2021-03-31T23:59:59.997'

SELECT DATEDIFF(DAY, '2021-03-01T00:00:00.000', '2021-03-31T23:59:59.999') + 1

SELECT DATEDIFF(DAY, @__dateRange_StartDate_4, @__dateRange_EndDate_3) + 1

SELECT @__dateRange_EndDate_3

(No column name)

31

(No column name)

31

(No column name)

2021-03-31 23:59:59.997