Date and Time Calculations for Prior Day Bracketing

Reduce, Reuse, Recycle

I’ve been touting lately in presentations at various SQL events that if you’re going to do something more than once to take time to script it out and save it for later.  I’ve been doing that using native Templates in Microsoft SQL Server Management Studio for years now.  Lately, however, I’ve also been employing Snippets available in Red Gate’s SQLPrompt product. As I work on my collection of recyclable code for a book I am mulling-over I will be posting out some of those templates & snippets that fit into my #SQLHacker initiative I blogged about here. This is one of those cases where this code is something I see people asking about frequently enough to release as a post here at The SQL Agent Man.

Bracketing Dates

Developers and Database Administrators alike are constantly dealing with queries that have to be date-bound in some fashion. I’m referring to start date / end date scenarios. I touched upon this topic from a different angle back in 2009 when I authored an article for MSSQLTips on the topic of finding a specific day of the week forward or backward in time (for instance the last Tuesday or five Mondays from now.) This time around I want to provide a quick script for determining a very common date range bracket when dealing with daily reporting.

Daily Reports Bracketing Functions for Start Date

Most of the daily reports I encounter encompass the time frame of Midnight yesterday until some terminus just shy of Midnight today. Below is the calculation I use to determine the start date of any daily report I build:

-- To Get Midnight Yesterday
2013-04-17 00:00:00.000

Daily Reports Bracketing Functions for End Date

Author’s Note:  Aaron Betrand raised a very valid point in the comments below and I’ve since come back here to refine the code I orginally presented.

Typically you’re going to bracket your daily reporting on the start and end of the previous day.  I’ve already shown you how to calculate the start predicate.  Now for end predicate.  Here the preference would be to simply use the same coding construct as presented above for start date but use midnight of the current day and then query for the records >= start time and < end time where that end time is midnight today:

>-- To Get Midnight Today
2013-04-18 00:00:00.000

You end up with the following as your base filtering clause as a result:

WHERE some_column >= DATEADD(d, -1, DATEDIFF(d, 0, GETDATE()))
     AND some_colum < DATEADD(d, 0, DATEDIFF(d, 0, GETDATE()))

What About Other Terminal Dates?

You can use similar code to get time slices for reports by tweaking the offset in the DATEADD function. For example you may wish to pull in records for Midnight yesterday until noon yesterday. Add an offset to the existing base code construct and it’s very easy to account for this option:

--Return Value for Noon Yesterday
2013-04-17 12:00:00.000

#SQLHacker Tips

Since this is one of my #SQLHacker posts we got down and dirty quick. Stay tuned here for more quick-hit tips for making your SQLlife easier. Also, if you’re a blogger, tag your posts with #SQLHacker and join the effort to provide easy, quick, and free solutions for today’s SQL Professional.

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