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tuka
Starting Member
26 Posts |
 Posted - 2010-04-28 : 05:18:30
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| Hi Just needed a bit of guidance:I am using code generated by MSSS management studio and what I get in an order table is (part):CREATE TABLE [dbo].[tblOrders]( [intID] [int] IDENTITY(1,1) NOT NULL,then at the bottom it has CONSTRAINT [PK_tblOrders] PRIMARY KEY CLUSTERED shouldn't CLUSTERED be UNIQUE since we are especting unique intergers ids in field intID ?TIA |
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SwePeso
Patron Saint of Lost Yaks
30421 Posts |
Posted - 2010-04-28 : 05:36:20
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Primary key indexes are per definition unique.With the exception that UNIQUE indexes allow one NULL value where PRIMARY KEY indexes allow none NULL value.
N 56°04'39.26"E 12°55'05.63" |
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visakh16
Very Important crosS Applying yaK Herder
52326 Posts |
Posted - 2010-04-28 : 05:46:45
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| PRIMARY KEYs have additional condition that they wont allow a NULL value apart from being unique------------------------------------------------------------------------------------------------------SQL Server MVPhttp://visakhm.blogspot.com/ |
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Transact Charlie
Master Smack Fu Yak Hacker
3451 Posts |
Posted - 2010-04-28 : 06:22:58
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| Just to add a little to Peso and visakh16's reply. Apologies if you know all this stuff already.The CLUSTERED keyword here indicates that the PRIMARY KEY should be implemented with a clustered index. You can only have one clustered index per table and it alters the layout of the data. Imagine a phone book. the CLUSTERED INDEX of the phone book is surname, firstname, address. (The data is physically layed out in that order. Obviously that makes it very easy to find the phone number for someone if you know their name.You can declare a PRIMARY KEY with the NONCLUSTERED hint. This makes a NONCLUSTERED INDEX over the primary key column(s). A nonclustered index is like a lookup list pointing to the data. (like the index at the back of a catalogue that lets you find the correct page number for something you want to buy for example).The PRIMARY KEY indicates that the column must be unique. (it uniquely identifies a row in the table). The NONCLUSTERED / CLUSTERED keyword determines which sort of index the key uses.Charlie===============================================================Msg 3903, Level 16, State 1, Line 1736The ROLLBACK TRANSACTION request has no corresponding BEGIN TRANSACTION |
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CLUSTERED or UNIQUE constraint ?