Question

MyTable:
 id     int
 Date1  DateTime
 Date2  DateTime

How can I set the time of Date2 to be the same as Date1 without affecting the date of Date2?

Answer 1

Update Date2 with only the difference in days between the two dates.

UPDATE MyTable
SET Date2 = DATEADD(DAY, DATEDIFF(DAY, Date1, Date2), Date1);

This will preserve the date portion of Date2.

UPDATE: This method essentially reconstructs Date2 by using Date1 as a reference and only adding the difference in days between Date1 and Date2 – preserving the TimeStamp from Date1.