Updating a DateTime field in SQL Server db from Date and Time fields

Question

In a SQL Server 2008 database I have a table with a Date field of datatype date and a Time field of datatype time. The table contains some data.

Then I added a DateTime field of datatype datetime and wanted to populate this field with values from corresponding Data and Time fields (of the same row).

I can update either date or time part of DateTime field by executing:

SET [DateTime] = Cast([Date] as datetime)

or

SET [DateTime] = Cast([Time] as datetime)

But how to correctly combine these operations and update the whole DateTime field?

Answer 1

UPDATE  mytable
SET     [DateTime] = CAST([Date] AS DATETIME) + CAST([Time] AS DATETIME)