Combining (concatenating) date and time into a datetime

An easier solution (tested on SQL Server 2014 SP1 CU6)

Code:

DECLARE @Date date = SYSDATETIME();

DECLARE @Time time(0) = SYSDATETIME();

SELECT CAST(CONCAT(@Date, ' ', @Time) AS datetime2(0));

This would also work given a table with a specific date and a specific time field. I use this method frequently given that we have vendor data that uses date and time in two separate fields.

Assuming the underlying data types are date/time/datetime types:

SELECT CONVERT(DATETIME, CONVERT(CHAR(8), CollectionDate, 112) 
  + ' ' + CONVERT(CHAR(8), CollectionTime, 108))
  FROM dbo.whatever;

This will convert CollectionDate and CollectionTime to char sequences, combine them, and then convert them to a datetime.

The parameters to CONVERT are data_type, expression and the optional style (see syntax documentation).

The date and time style value 112 converts to an ISO yyyymmdd format. The style value 108 converts to hh:mi:ss format. Evidently both are 8 characters long which is why the data_type is CHAR(8) for both.

The resulting combined char sequence is in format yyyymmdd hh:mi:ss and then converted to a datetime.

The simple solution

SELECT CAST(CollectionDate as DATETIME) + CAST(CollectionTime as DATETIME)
FROM field