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 Posted Tuesday, July 02, 2013 4:23 PM
 SSCommitted Group: General Forum Members Last Login: Tuesday, January 21, 2014 8:55 AM Points: 1,520, Visits: 3,035
 Here's another example of using the AND (&) operator to query an integer being used as a bit-map. You may have a set of integers, each representing the calendar for a month. You can set bits in each to indicate certain days, perhaps weekends and holidays. For this month, July 2013, here in the U.S. we would set the bits for the four weekends and for the holiday on the fourth of July. Then, we can use the & operator to query whether a particular date in the month is not a business day:`declare @monthCalendar int set @monthCalendar = power(2,4) -- set bits for the holiday and the four weekends + power(2,6) + power(2,7) + power(2,13) + power(2,14) + power(2,20) + power(2,21) + power(2,27) + power(2,28)declare @dateInMonth intset @dateInMonth = 4 -- check this date in the monthdeclare @dateBitValue intset @dateBitValue = power(2,@dateInMonth) Select @monthCalendar as MonthCalendar -- this integer may have been stored in your db somewhere ,Case when @monthCalendar & @dateBitValue > 0 then 'Yes' Else 'No' end as DateIsSelected`
Post #1469786
 Posted Tuesday, July 02, 2013 10:20 PM
 SSChasing Mays Group: General Forum Members Last Login: Friday, February 14, 2014 4:11 AM Points: 602, Visits: 133
 Nice question and discussion.....
Post #1469839
 Posted Wednesday, July 03, 2013 8:29 AM
 Mr or Mrs. 500 Group: General Forum Members Last Login: Today @ 8:45 AM Points: 577, Visits: 710
 I use this methodology to establish a system of Rights for Users in applications. Using BIGINT you can have a total of 63 different individual Rights assigned to a User all contained in a single BIGINT column value. Very compact and very fast for retrieval and using masks for determining if the User has a specific right or not.Bill
Post #1470088
 Posted Wednesday, July 03, 2013 10:01 AM
 Valued Member Group: General Forum Members Last Login: Wednesday, February 19, 2014 1:53 AM Points: 60, Visits: 372
 In SQL you have several options to associate a set with a row for a multi-valued attribute of an entity. The most obvious solution is a separate table that stores a foreign key to the original row along with a single (reference to a) value of the attribute in each row. You can add an XML column and store several attribute values inside it (even for different attributes) but storing and retrieving their value introduces some overhead and additional complexity to your queries. If the number of values for a single row is rather limited, a numbered column collection is also an option ([TelNr_1], [TelNr_2], [TelNr_3], ...) though I would personally never recommend this solution. If the total number of possible values is very limited you might use a bitmap where each bit represents a value and that bit is set if the multi-valued attribute contains that value. A separate table should map the individual bits to the actual values.If you can live with the limitations of a bitmap (no foreign key and at most 64 values) it will save some storage but more important it allows you to do all kinds of set operations using simple bitwise operations. Checking wether the intersection of two sets is not empty requires no more than a bitwise and and a comparison. A bitwise or creates the union of two sets, an exclusive or the symmetric difference and an and with a not the difference. Allowing fast set operations makes these bitmaps extremely useful in authorization schemes. You should add the bitmap to your tool belt but use it with care, because it obscures the actual relations between tables and might cause serious trouble as soon as the number of possible values (roles for example) suddenly grows above that magic limit of 64.Although there is no physical relation between the table with the bitmap attribute and the table that maps the individual bits (guarded by a foreign key), a logical relation between these tables does exist. Fortunately SQL Server allows us to define any join predicate we like, so instead of an eqi-join we may use a bitwise and as well: [OriginalTable] INNER JOIN [ValueTable] ON ([OriginalTable].[Bitmap] & [ValueTable].[IndividualBit]) <> 0. A subquery with a FOR XML clause and a few REPLACEs around it can turn your bitmap into a human-readable comma-separated list of attribute values.
Post #1470143
 Posted Wednesday, July 03, 2013 10:53 AM
 SSC Veteran Group: General Forum Members Last Login: Monday, March 10, 2014 1:30 PM Points: 240, Visits: 208
 Wow... One thing about Bitwise operaters is certain.It is easy to read these posts and know who understands them completely and who is lost.This would make for a great Article... Especialy the is BIGINT supported part.... Hrmmmmm
Post #1470162
 Posted Thursday, July 04, 2013 4:08 AM
 SSC Rookie Group: General Forum Members Last Login: Tuesday, February 11, 2014 10:46 AM Points: 31, Visits: 60
 I think that the best example here is @@OPTIONS.You do need the Bitwise AND operator if you're using it.
Post #1470384
 Posted Thursday, July 04, 2013 3:19 PM
 SSCarpal Tunnel Group: General Forum Members Last Login: Today @ 4:58 PM Points: 4,176, Visits: 3,251
 PHYData DBA (7/3/2013)Wow... One thing about Bitwise operaters is certain.It is easy to read these posts and know who understands them completely and who is lost.This would make for a great Article... Especialy the is BIGINT supported part.... Hrmmmmm I wrote this QotD when I found that one of the members of my team did not understand that you could do AND on operands of a different length. I thought that the SQLServerCentral audience could benefit, and I hope we all did.
Post #1470514
 Posted Tuesday, July 09, 2013 3:29 AM
 Hall of Fame Group: General Forum Members Last Login: 2 days ago @ 1:57 AM Points: 3,505, Visits: 2,603
 It was a good basic question.
Post #1471500
 Posted Thursday, July 25, 2013 9:22 AM
 SSC-Insane Group: General Forum Members Last Login: Today @ 7:42 PM Points: 20,254, Visits: 13,807
 raulggonzalez (7/2/2013)Danny Ocean (7/1/2013)Good question. But i never feel to use "Bitwise AND" (&) in real working scenario. It will good, if anyone come with some real working example. Hi, another example where BIT comparison is useful, msdb..sysschedules keeps the freq_interval in bitwise value :)`use [msdb]gocreate table #DaysOfWeekBitWise( [bitValue] [tinyint] NOT NULL PRIMARY KEY, [name] [varchar](10) NULL,) goinsert into #DaysOfWeekBitWise ([bitValue], [name]) values (1, N'Sunday') , (2, N'Monday') , (4, N'Tuesday') , (8, N'Wednesday') , (16, N'Thursday') , (32, N'Friday') , (64, N'Saturday')goselect j.name , case when j.enabled = 1 then 'Yes' else 'No' end as enabled , jsch.next_run_date , jsch.next_run_time --, jst.* , s.freq_interval , ISNULL( STUFF( (SELECT N', ' + name FROM #DaysOfWeekBitWise AS B WHERE B.bitValue & s.freq_interval = B.bitValue FOR XML PATH('') ), 1, 2, '' ), 'None' ) AS backup_schedule from msdb.dbo.sysjobs as j left join msdb.dbo.sysjobschedules as jsch on jsch.job_id = j.job_id left join msdb.dbo.sysschedules as s on s.schedule_id = jsch.schedule_id order by j.namegodrop table #DaysOfWeekBitWisego`CheersAnother good example is with Reporting Services and Subscriptions Jason AKA CirqueDeSQLeilI have given a name to my pain...MCM SQL ServerSQL RNNRPosting Performance Based Questions - Gail ShawPosting Data Etiquette - Jeff ModenHidden RBAR - Jeff ModenVLFs and the Tran Log - Kimberly Tripp
Post #1477569

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