DATETIME compare issue

Question

I am trying to do a select where one set of date/time columns are greater than another.  My date is stored in one column while the time is stored in another.  Only the date portion of the date column is valid and only the time portion of the time column is valid.
Example  my date column value is 8/1/2007 01:01:01 AM and my time column value is 1/1/2007 07:23:49 AM which in my system means the last update time was 8/1/2007 07:23:49 AM.
My select statment looks like this.
SELECT  *
FROM         CHANGE
WHERE
CONVERT(DATETIME( DATE_LAST_ALTERED, TIME_LAST_ALTERED)) < CONVERT(DATETIME(DATE_APPROVED,TIME_APPROVED))
I get an incorrect syntax near 'DATE_LAST_ALTERED'.
Am I totaly missing the point of DATETIME?
Matt

Answer 1

You need to give a look to the CAST AND CONVERT article in books online; your syntax for your CONVERT function is not correct.  And yes, you might very well be missing the point of date and time in SQL Server.  You should normally store date and time in a single column.  And your usage here surely indicates that your date and time should be stored in a single column.  You might be able to run with a where clause something like:
Code Snippet
where cast(floor(cast(date_last_altered as float)) as datetime)
        + time_last_altered
        - floor(cast(time_last_altered) as float))
    < cast(floor(cast(date_approved as float)) as datetime)
        + time_approved
        - floor(cast(time_approved) as float))
Will someone please check me please?