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Disabling Indexes


Disabling Indexes

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croberts 36762
croberts 36762
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Oops. I figured it out.
marklegosz
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The explaination was very interesting (which I learned from) but I felt the question didn't really illistrate the point very well, i.e. the net result was drop an index and run a select on the table. Who would have thought select * from table returns all rows.
SQLRNNR
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Thanks for the question

Jason...AKA CirqueDeSQLeil
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Nakul Vachhrajani
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Hello!

Thank-you all for your kind comments and feedback.

I am sorry that a few of you did have some trouble trying to get the code running on your servers. I also apologize for not having the time during the day to reply to all who took the time out to comment (had a busy day at home and at office today).

What fascinated me the most about this was that it taught me a little something about constraints and how SQL Server uses them (i.e. the use of the constraint made SQL look for the index, which was disabled).

To all those who read the question and took the time to attempt it - a very big thank-you from me. To all those who learnt something new, SQL is magical and this question is even more motivation to learn more about it!

Have a wonderful weekend ahead!

Thanks & Regards,
Nakul Vachhrajani.
http://nakulvachhrajani.com
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Nadrek
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SanjayAttray (9/10/2010)
Good question. I had not disabled index as of now or never tried. Thought that it would fetch data but would take time, period.


Same here; but I've seen countless disabled constraints, as well as enabled but Untrusted constraints.
rals
rals
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Thanks for the nice question.

It would have been tough if you didn't have "-- Drop the associated constraints" in the statements.

Regards,
Rals
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Nakul Vachhrajani
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Hello!

The goal of this question was to have a deeper understanding of how SQL Server behaves, and not making the questions harder. Emphasis is therefore on the fact that if we have the constraints enabled, SQL does try to use the index which it cannot do because it's disabled. If one knows this concept, the answer is "easy" - otherwise it's "difficult"/"harder".

Thanks & Regards,
Nakul Vachhrajani.
http://nakulvachhrajani.com
Be courteous. Drive responsibly.

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rals
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Yes nakul...

Regards,
Rals
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Hugo Kornelis
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Nakul Vachhrajani (9/13/2010)
Emphasis is therefore on the fact that if we have the constraints enabled, SQL does try to use the index which it cannot do because it's disabled.

Actually, the reason you get an error if the index is disabled is that, for a clustered index, the index IS the table. As a result, disabling the clustered index equates to disabling the table.

If you use a nonclustered rather than a clustered index, then table is still accessible even with the index disabled. You can try this for yourself, by simply changing the "CLUSTERED" to "NONCLUSTERED" in the constraint declaration for the primary key.


Hugo Kornelis, SQL Server/Data Platform MVP (2006-2016)
Visit my SQL Server blog: http://sqlblog.com/blogs/hugo_kornelis
Koen Verbeeck
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Nice question. Thanks...


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