alter column on a large table taking too long

I have a table with 80 million rows of data. I want to alter data type of one of the columns on this table (varchar to numeric), but the alter column sql has been running for an hour now, still not done, and has a lock on the table. Is there a faster way to alter column on a large table.

Thanks for your help.
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Kanti PrasadCommented:

Try to create a new table like the old one and then alter the new one and insert data from the old table into the new one and then rename the old table and then rename the new table to the old one and then delete the renamed old table.

Here is a link that will give you an idea

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Randy PooleCommented:
Normally you would place the database into single user mode.
Aneesh RetnakaranDatabase AdministratorCommented:
If its already running, you can wait till it finishes.  Otherwise  As Kanti Prasad Mentioned, you can try creating another table with the new structure and populate the data;
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patd1Author Commented:
Thanks for your suggestions.

I cancelled the query after waiting for too long, but now it is in "cancelling" mode for a long time. Is there a way i can make it cancel faster so I can work on creating new table /move data and rename as suggested.

Thank you again.
Randy PooleCommented:
Not without compromising the data.
QlemoBatchelor, Developer and EE Topic AdvisorCommented:
Cancelling the operation might have been worse than allowing it to finish. All changes made up to now need to get rolled back - a more costly operation than the operation itself usually.
patd1Author Commented:
The disk IO was only showing 5 million, while the whole table is 80 million rows. Completing it would have take a couple days at that speed.
QlemoBatchelor, Developer and EE Topic AdvisorCommented:
Always difficult to tell whether you should cancel or let go,  but in that case I would have cancelled too probably. Be prepared to wait at least twice the time it took to get there for rolling back.
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Microsoft SQL Server 2008

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