I have a table with some bad data in SQL. this table has a lot of relationship with other tables and other tables have a lot of data so when I want to delete bad data it's very slowly and take lots of time to do. I think the cause of this problem is foreign key constraints. the main problem is how can disable all of the foreign key constraints from one table.
You have to disable check constraint:
SET FOREIGN_KEY_CHECKS=0;
Make sure to turn it back after your commands:
SET FOREIGN_KEY_CHECKS=1;
Disable constraint for one table:
alter table
table_name
DISABLE constraint
constraint_name;
Here is an example:
select 'alter table '||table_name||' disable constraint '||constraint_name||';' from user_constraints;
Related
I have the problem similar to this one SQL Server foreign key conflict in a multi values statement? However, in sql server 2008.
While I am reading data from csv file, there is some id already not exist in parent and thus return this error:
INSERT statement conflicted with the FOREIGN KEY constraint
May I know if there is a way similar to MySQL insert ignore. Such that I can simply skip the problematic data.
I accept that if there is no method other than creating a stored procedure with a new temp table (insert into a table without foreign key first, and then re-insert with where foreign_id exists in (select id from parent)).
As I really cannot find any in documentation, asking for ensuring I didn't miss anything.
One general solution which comes to mind would be to temporarily turn off the foreign key constraints, and do the insert. Then, afterwards, you may run a cleanup script/query to remove or rectify child records which are pointing to parents which do not exist. Once your data is in good shape, then turn on the foreign key constraints again.
Read How can foreign key constraints be temporarily disabled using T-SQL? to learn how to disable/enable a foreign key constraint for a single table:
ALTER TABLE MyTable NOCHECK CONSTRAINT MyConstraint -- disable
ALTER TABLE MyTable WITH CHECK CHECK CONSTRAINT MyConstraint -- enable
While generating the Create DB script for the existing Foreign Key constraint through SSMS, we could able to see two set of alter statements. one with NOCHECK ADD and another with CHECK.
ALTER TABLE [dbo].[claim] WITH NOCHECK ADD CONSTRAINT [FK_CLAIM_COPCID]
FOREIGN KEY([copcid])
REFERENCES [dbo].[copc] ([CopcId])
GO
ALTER TABLE [dbo].[claim] CHECK CONSTRAINT [FK_CLAIM_COPCID]
GO
Why we are getting two set of scripts to create a new Constraint?.
The first alter statement is creating a constraint and instructing that constraint to be added without checking whether the existing rows obey the new constraint.
When you add a constraint without first checking the rows, it will not be fully active until you enable it. That's what the second statement does, it enables the new constraint. If there are rows that break the constraint, you won't be able to enable it.
In my table I have primary key on 3 columns (name, dept, MobNo).
Now I want to change it to be on two columns (Name, MobNo).
Is there any way I can alter the primary key constraint without dropping it?
I know I can drop old constraint and can create new but without dropping old constraint it is possible to alter it?
The only and one way would be to drop the constraint with an Alter table then recreate it.
ALTER TABLE <Table_Name>
DROP CONSTRAINT <constraint_name>
ALTER TABLE <Table_Name>
ADD CONSTRAINT <constraint_name> PRIMARY KEY (<Column1>,<Column2>)
If you (probably) have dependencies on that PK, you will also have to drop them and recreate them. To have all this done automagically, it's easier from SSMS to right-click on the table, choose Design, and from there you click in the top left toolbar the button called Manage indexes and Keys. From there you make your changes, and at the end, you have 2 options:
you close and save your changes (and it works fine but you don't learn anything)
instead you click on the Generate change script so you can examine and execute the script later
(at least it works like this with my version 2014 of SSMS)
When I have issued a
ALTER TABLE table DISABLE CONSTRAINT fk1
and when I then try to drop the table
DROP TABLE table
That the constraint is still checked even though it is disabled.
Have I missed something?
You have to drop the constraints as well in order drop a table. Try the following:
DROP TABLE someTable CASCADE CONSTRAINTS;
DISABLE CONSTRAINT works for update/insert statements.
See oracle help.
Disabling Constraints
To enforce the rules defined by integrity constraints, the constraints
should always be enabled. However, consider temporarily disabling the
integrity constraints of a table for the following performance
reasons:
When loading large amounts of data into a table
When performing batch operations that make massive changes to a table
(for example, changing every employee's number by adding 1000 to the
existing number)
When importing or exporting one table at a time
You are trying to drop your table. It is not designed to for this. You need to DROP CONSTRAINTs.
I am about to run a massive data insert into my DB. I have managed to work out how to enable and rebuild non-clustered indexes on my tables but I also want to disable/enable primary keys as I believe this will speed up the insertion process.
NOTE: This is over numerous tables and so I assume I need some loop to get the primary key information and run the following to drop it but I'm not sure about recreating it:
ALTER TABLE Table1
DROP CONSTRAINT PK_Table1_Col1
IIRC clustered indexes cannot be disabled as they govern where the actual data is stored in the pages.
I'm pretty sure you would have to drop the key and re-create it after your insert. Depending on the size of the tables, indexes and insert this may not save you any time.
Run This :
//For disable all constraint of your all tables
exec sp_MSforeachtable 'ALTER TABLE ? NOCHECK CONSTRAINT ALL'
//Your insert query here ......................
//After Insert Enable all the constraint
exec sp_MSforeachtable 'ALTER TABLE ? CHECK CONSTRAINT ALL'