[sql-server] How to get first and last day of previous month (with timestamp) in SQL Server

Take some base date which is the 31st of some month e.g. '20011231'. Then use the
following procedure (I have given 3 identical examples below, only the @dt value differs).

declare @dt datetime;

set @dt = '20140312'

SELECT DATEADD(month, DATEDIFF(month, '20011231', @dt), '20011231');



set @dt = '20140208'

SELECT DATEADD(month, DATEDIFF(month, '20011231', @dt), '20011231');



set @dt = '20140405'

SELECT DATEADD(month, DATEDIFF(month, '20011231', @dt), '20011231');