Careful, that won't be guaranteed to be correct if the data is ever changed to datetime2 with a higher precision than datetime.

Might as well use Jeff's, which will work regardless of the data type.

DECLARE @PreviousMonthStart DATETIME

DECLARE @PreviousMonthEnd DATETIME

SET @PreviousMonthStart = DATEADD(m,DATEDIFF(m,0,GETDATE())-1,0);

SET @PreviousMonthEnd = DATEADD(ms,-2,DATEADD(month, DATEDIFF(month, 0, GETDATE()), 0));

PRINT @PreviousMonthStart;

PRINT @PreviousMonthEnd;

CREATE TABLE #MyTable (MyDate datetime2(3), some_string varchar(100));

INSERT INTO #MyTable VALUES

('20160301 12:39:10.898','This one is fine.'),

('20160331 23:59:59.999','What about me? Sniff sniff');

--This one is only guaranteed to return

--correct results for datetime

SELECT * FROM #MyTable

WHERE MyDate >= @PreviousMonthStart

AND MyDate < @PreviousMonthEnd;

--Jeff's will always work

SELECT * FROM #MyTable

WHERE MyDate >= DATEADD(mm,DATEDIFF(mm,0,GETDATE())-1,0)

AND MyDate < DATEADD(mm,DATEDIFF(mm,0,GETDATE()),0);

DROP TABLE #MyTable;

Cheers!