Solved

multiple unique columns in a table

Posted on 2011-09-16
8
385 Views
Last Modified: 2012-05-12
can we have multiple unique columns in a table. I was not clear on this concept. Please advise. thanks in advance
0
Comment
Question by:gudii9
8 Comments
 
LVL 47

Expert Comment

by:for_yan
ID: 36552810
you can have multiple unique columns in a table - there is nothing that may prevent it
0
 
LVL 47

Accepted Solution

by:
for_yan earned 125 total points
ID: 36552821
Let's say you have the table of patients of the hospital - they may have their own id for each patient , but they may have a column for insusrance id and those
may be also be unique - certainly no problem with that
0
 
LVL 37

Assisted Solution

by:momi_sabag
momi_sabag earned 125 total points
ID: 36552830
you can have as many unique constraint you want on a table
a unique constraint verify that a column or set of columns have unique values in every row in a table
0
PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

 
LVL 21

Assisted Solution

by:Amitkumar Panchal
Amitkumar Panchal earned 125 total points
ID: 36553738
Yes, You can have unique constraint on the all fields of the table. Only thing is that if the column having unique constraint must contains a unique value in that field across the table. However, the field contains a null (no value) value in it, so multiple null values are allowed in the field having a  unique constraint.
0
 
LVL 45

Assisted Solution

by:Kent Olsen
Kent Olsen earned 125 total points
ID: 36553894
Hi gudi,

The easiest way to enforce multiple unique columns in a table is to put a unique index on each of the columns.  

In fact, if you have a significant amount of data in the table it will be almost imperative to have these columns indexed as every insert or update will need to verify that the new data is unique within the column.  Without indexes on these column a full table scan will be required just to insert a new row!


Good Luck,
Kent
0
 
LVL 7

Author Comment

by:gudii9
ID: 36718886
How to put  unique index on each column
0
 
LVL 47

Expert Comment

by:for_yan
ID: 36718899
you can create index for any column or you can impose unique constraint on each colimn -
thes are different things
0
 
LVL 45

Expert Comment

by:Kent Olsen
ID: 36718913
Hi gudi,

You'll need to add the index or constraint for each column that must be unique.

CREATE UNIQUE INDEX idx0001 ON mytable (column1);
CREATE UNIQUE INDEX idx0002 ON mytable (column2);
etc....



Kent
0

Featured Post

How Do You Stack Up Against Your Peers?

With today’s modern enterprise so dependent on digital infrastructures, the impact of major incidents has increased dramatically. Grab the report now to gain insight into how your organization ranks against your peers and learn best-in-class strategies to resolve incidents.

Question has a verified solution.

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

Introduction This article is the second of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article covers the basic installation and configuration of the test automation tools used by…
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
This video shows syntax for various backup options while discussing how the different basic backup types work.  It explains how to take full backups, incremental level 0 backups, incremental level 1 backups in both differential and cumulative mode a…
This theoretical tutorial explains exceptions, reasons for exceptions, different categories of exception and exception hierarchy.

840 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