Question

I have two columns in DB: StartDate (datetime column) and StartTime (nvarchar column).
StartDate contains date when event shoud start.
StartTime contains time when event should start. It is 24hour format (for example, 22:00 or 12:00).

I need to combine StartDate with StarTime to use it in WHERE clause and compare the result with variable. It would look like:

WHERE COMBINED_STARTDATE_WITH_STARTIME >= @DATETIME_VARIABLE

I am using SQL SERVER 2008.
This is existing DB design and would not like to change it. Probably, I can create third column and combine datetime + startdate into one column, but I am looking for another sollutions (that doesn’t touch database).

Answer 1

You can use something like this:

WHERE 
dateadd(minute, cast(right(starttime, 2) as int),
    dateadd(hour, cast(left(starttime, 2) as int), startdate)) >= @DATETIME_VARIABLE

SQL Fiddle with DateTime Conversion

In the event the start time is null then you can use IsNull() around the value:

WHERE
dateadd(minute, cast(right(isnull(starttime, 0), 2) as int),
    dateadd(hour, cast(left(isnull(starttime, 0), 2) as int), startdate)) >= @DATETIME_VARIABLE

See SQL Fiddle with Demo

Of course if you are using SQL Server 2008+ you can just cast your value as time:

WHERE startdate + IsNull(StartTime, '00:00') >= @DATETIME_VARIABLE

See SQL Fiddle with Demo