Solved

drop index does not work for unique keys

Posted on 2010-08-19
8
277 Views
Last Modified: 2012-05-10
what is the reason DROP index syntax is disabled for deleting unique keys (non PKs)

thanks
0
Comment
Question by:anushahanna
  • 4
  • 3
8 Comments
 
LVL 142

Assisted Solution

by:Guy Hengel [angelIII / a3]
Guy Hengel [angelIII / a3] earned 425 total points
ID: 33474819
this is because the PK is relying on the underlying index for it's function.

imagine you had a 2GB table with a primary key, but no index on that column.
the primary key constraint would have to do a full table scan for each insert & update for that field value !!!
0
 
LVL 18

Assisted Solution

by:Cluskitt
Cluskitt earned 75 total points
ID: 33474894
If you want to drop the index (possibly for rebuilding it), then drop the constraint first.
0
 
LVL 6

Author Comment

by:anushahanna
ID: 33475442
>>this is because the PK is relying on the underlying index for it's function.

even if PK and UK are both different? (example PK is on Col1 and UK is on Col3..)
0
 
LVL 142

Accepted Solution

by:
Guy Hengel [angelIII / a3] earned 425 total points
ID: 33475652
if you have a PK and a UK, you will also have 2 indexes, 1 index per UK or PK constraint.
for the rest, it's the same situation: the database engine will not allow to drop the index.
0
Zoho SalesIQ

Hassle-free live chat software re-imagined for business growth. 2 users, always free.

 
LVL 6

Author Comment

by:anushahanna
ID: 33476646
are you saying PK will be relying on the unique index, regardless if they are the same or 2 diff indexes?
0
 
LVL 6

Author Comment

by:anushahanna
ID: 33476973
will DROP INDEX syntax work sometimes and othertimes not, for UNIQUE Indexes?
0
 
LVL 142

Assisted Solution

by:Guy Hengel [angelIII / a3]
Guy Hengel [angelIII / a3] earned 425 total points
ID: 33479687
>are you saying PK will be relying on the unique index, regardless if they are the same or 2 diff indexes?

no. let me clarify:
when you create a PK, sql server will create automatically create a index, for that PK constraint. and it will not let you drop that index.

when you create a UC (unique constraint), sql server will create automatically create a index, for that UC constraint. and it will not let you drop that index.

when you create whatever index, they will NOT be used for any PK or UC, and sql will let your drop that index without issues
this includes also unique indexes, as they are not created by a constraint as such

0
 
LVL 6

Author Comment

by:anushahanna
ID: 33484609
thanks angelIII, for the helpful explanation.
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

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

JSON is being used more and more, besides XML, and you surely wanted to parse the data out into SQL instead of doing it in some Javascript. The below function in SQL Server can do the job for you, returning a quick table with the parsed data.
Slowly Changing Dimension Transformation component in data task flow is very useful for us to manage and control how data changes in SSIS.
This video shows, step by step, how to configure Oracle Heterogeneous Services via the Generic Gateway Agent in order to make a connection from an Oracle session and access a remote SQL Server database table.
Via a live example, show how to extract information from SQL Server on Database, Connection and Server properties

910 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

Need Help in Real-Time?

Connect with top rated Experts

22 Experts available now in Live!

Get 1:1 Help Now