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Question on constrains

Posted on 2011-02-23
Last Modified: 2012-06-21
I have two databases I am trying to sync with RedGate's  SQL Compare.
Objects such as tables have slight differences and thats OK, but one database has one constrain in that object and another has a different constrain in the same object. Don't ask me why.

Question:  What happens if I drop the constrains on both databases so I can run my sync ?
Question: Is there a way to drop ALL constrains in all tables of a database, if so .. how ?  if not, how do I drop constrains from one table ?
Question: What could happen if I drop constrins from one table

My constrains look something similar to:




I am using MS SQL 2008 Server
Question by:amucinobluedot
LVL 39

Expert Comment

ID: 34964598
You could get duplicate ID's and that's not good from data integrity point of view.
LVL 39

Accepted Solution

lcohan earned 250 total points
ID: 34964624
You could generate/run some scripts to save all constraints definition, drop them, do the work you want and:

a. add them back WITH CHECK to revalidate data integrity
b. if you don't care about data integrity you could add them WITH NOCHECK leaving orphans and/or duplicates in tables.

Of course all these are NOT to be done on live production databases.

Author Comment

ID: 34964660
What would i need to do to drop one specific constrain ?
Not a key, but another constrain, such as:

-- Foreign Keys

ALTER TABLE [dbo].[ActivityParties] WITH NOCHECK ADD FOREIGN KEY ([activity_id]) REFERENCES [dbo].[Activities] ([ActivityId]) ON DELETE CASCADE


What is the difference between a 'clustered' and a nonclustered key ?

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LVL 15

Assisted Solution

derekkromm earned 125 total points
ID: 34965812
a clustered index indicates the order in which the table physically stores data

a nonclustered index indicates an ordering cache, per se

so if you have a table with columns A, B, and C, and its clustered on A, it is physically storing the data ordered by A. however, you can also have a nonclustered index on C so that you can easily seek the data on C (for example, if C has dates and you frequently select data from the table based on a range of dates)
LVL 15

Expert Comment

ID: 34965816
to drop constraints, you simply do

alter table <table> drop constraint <constraint name>
LVL 75

Assisted Solution

by:Anthony Perkins
Anthony Perkins earned 125 total points
ID: 34967091
Perhaps I am stating the obvious, but you do realize that SQL Compare will generate all the DROP/CREATE statements necessary in order to sync the tables.  There is no need for you to do that.  Just decide how you want them and then go for it.

Incidentally, not sure if that was a typo, but those two constraints appear to be on different tables.
LVL 39

Assisted Solution

lcohan earned 250 total points
ID: 34970147
And from performance point of view - dropping a CLUSTERED "constraint" will be quick especially if db is not live under load however to add it back on large tables.....different story. Good luck.

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