Solved

Confusion about documentation in BOL with regard to "Ignore duplicate key".

Posted on 2006-10-24
6
302 Views
Last Modified: 2008-01-09
Hi.

BOL | Using the SQL Server Tools | User Interface Reference | Visual Database Tools | Properties Page | Database Designer Properties Page | Index/Keys Property Page says ...

[snip]
Create UNIQUE
Select this option to create a unique constraint or index for the selected database table. Specify whether you are creating a constraint or index by selecting either the Constraint or Index button.

Ignore duplicate key   If you create a unique index, you can set this option to ensure each value in an indexed column is unique.
[snip]

What will happen if you 2 rows with the same value for the key column(s)?

0
Comment
Question by:Richard Quadling
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 3
6 Comments
 
LVL 10

Expert Comment

by:AaronAbend
ID: 17795526
the second row will not be added
0
 
LVL 40

Author Comment

by:Richard Quadling
ID: 17795538
How do I prove that? Is there an index dump facility?
0
 
LVL 10

Accepted Solution

by:
AaronAbend earned 150 total points
ID: 17795612
Insert a dup value - you do not need to see the index - just look at the data in the table...

create table ab(a int )
create unique index adbab on ab(a)   WITH( IGNORE_DUP_KEY = ON)

insert ab select 1
insert ab select 1

... messages:

(1 row(s) affected)

Duplicate key was ignored.
(0 row(s) affected)

0
Optimizing Cloud Backup for Low Bandwidth

With cloud storage prices going down a growing number of SMBs start to use it for backup storage. Unfortunately, business data volume rarely fits the average Internet speed. This article provides an overview of main Internet speed challenges and reveals backup best practices.

 
LVL 40

Author Comment

by:Richard Quadling
ID: 17796108
Ah. So the index restricts the insertion of data. What about adding the index to existing data?

(More points as the discussion has wandered a little).
0
 
LVL 10

Assisted Solution

by:AaronAbend
AaronAbend earned 150 total points
ID: 17796532
No.. a unique index normally prevents a duplicate value from being entered by issuing an error message. But ignore_dup_key causes that message to go away - but it does not let a duplicate into the table.

If you have an existing table, you can create an index...


create unique index myindexname on mytable(mycol1, mycol2, ...)

and if there are values that duplicate the index build will fail.

In SQL we do not look at indexes directly - they are stored in the database and they are used by the optimizer to speed up queries. You can see which indexes are being used by showing the execution plan in a query analyzer.

A clustered index actually resorts the table itself - so in effect you are looking at the index when you look at data in a table that has a clustered index, but that's not a very important thing to know.

0
 
LVL 40

Author Comment

by:Richard Quadling
ID: 17801535
That's great. Confirming some of the bits of knowledge I had.

Ta!
0

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Load balancing is the method of dividing the total amount of work performed by one computer between two or more computers. Its aim is to get more work done in the same amount of time, ensuring that all the users get served faster.
In this article we will learn how to fix  “Cannot install SQL Server 2014 Service Pack 2: Unable to install windows installer msi file” error ?
Via a live example, show how to setup several different housekeeping processes for a SQL Server.
Viewers will learn how the fundamental information of how to create a table.

726 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question