[sql-server] Temporarily disable all foreign key constraints

I am running an SSIS package which will replace data for a few tables from FlatFiles to existing tables in a database.

My package will truncate the tables and then insert the new data. When I run my SSIS package, I get an exception because of the foreign keys.

Can I disable the constraints, run my import, then re-enable them?

Disable all table constraints

ALTER TABLE TableName NOCHECK CONSTRAINT ConstraintName

-- Enable all table constraints

ALTER TABLE TableName CHECK CONSTRAINT ConstraintName

not need to run queries to sidable FKs on sql. If you have a FK from table A to B, you should:

• delete data from table A
• delete data from table B
• insert data on B
• insert data on A

You can also tell the destination not to check constraints

In case you use a different database schemas than ".dbo" or your db is containing Pk´s, which are composed by several fields, please don´t use the the solution of Carter Medlin, otherwise you will damage your db!!!

When you are working with different schemas try this (don´t forget to make a backup of your database before!):

DECLARE @sql AS NVARCHAR(max)=''
select @sql = @sql +
    'ALTER INDEX ALL ON ' + SCHEMA_NAME( t.schema_id) +'.'+ '['+ t.[name] + '] DISABLE;'+CHAR(13)
from  
    sys.tables t
where type='u'

select @sql = @sql +
    'ALTER INDEX ' + i.[name] + ' ON ' + SCHEMA_NAME( t.schema_id) +'.'+'[' + t.[name] + '] REBUILD;'+CHAR(13)
from  
    sys.key_constraints i
join
    sys.tables t on i.parent_object_id=t.object_id
where     i.type='PK'

exec dbo.sp_executesql @sql;
go

After doing some Fk-free actions, you can switch back with

DECLARE @sql AS NVARCHAR(max)=''
select @sql = @sql +
    'ALTER INDEX ALL ON ' + SCHEMA_NAME( t.schema_id) +'.'+'[' +  t.[name] + '] REBUILD;'+CHAR(13)
from  
    sys.tables t
where type='u'
print @sql

exec dbo.sp_executesql @sql;
exec sp_msforeachtable "ALTER TABLE ? WITH NOCHECK CHECK CONSTRAINT ALL";

Truncating the table wont be possible even if you disable the foreign keys.so you can use delete command to remove all the records from the table,but be aware if you are using delete command for a table which consists of millions of records then your package will be slow and your transaction log size will increase and it may fill up your valuable disk space.

If you drop the constraints it may happen that you will fill up your table with unclean data and when you try to recreate the constraints it may not allow you to as it will give errors. so make sure that if you drop the constraints,you are loading data which are correctly related to each other and satisfy the constraint relations which you are going to recreate.

so please carefully think the pros and cons of each method and use it according to your requirements

A good reference is given at : http://msdn.microsoft.com/en-us/magazine/cc163442.aspx under the section "Disabling All Foreign Keys"

Inspired from it, an approach can be made by creating a temporary table and inserting the constraints in that table, and then dropping the constraints and then reapplying them from that temporary table. Enough said here is what i am talking about

 SET NOCOUNT ON

    DECLARE @temptable TABLE(
       Id INT PRIMARY KEY IDENTITY(1, 1),
       FKConstraintName VARCHAR(255),
       FKConstraintTableSchema VARCHAR(255),
       FKConstraintTableName VARCHAR(255),
       FKConstraintColumnName VARCHAR(255),
       PKConstraintName VARCHAR(255),
       PKConstraintTableSchema VARCHAR(255),
       PKConstraintTableName VARCHAR(255),
       PKConstraintColumnName VARCHAR(255)    
    )

    INSERT INTO @temptable(FKConstraintName, FKConstraintTableSchema, FKConstraintTableName, FKConstraintColumnName)
    SELECT 
       KeyColumnUsage.CONSTRAINT_NAME, 
       KeyColumnUsage.TABLE_SCHEMA, 
       KeyColumnUsage.TABLE_NAME, 
       KeyColumnUsage.COLUMN_NAME 
    FROM 
       INFORMATION_SCHEMA.KEY_COLUMN_USAGE KeyColumnUsage
          INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS TableConstraints
             ON KeyColumnUsage.CONSTRAINT_NAME = TableConstraints.CONSTRAINT_NAME
    WHERE
       TableConstraints.CONSTRAINT_TYPE = 'FOREIGN KEY'

    UPDATE @temptable SET
       PKConstraintName = UNIQUE_CONSTRAINT_NAME
    FROM 
       @temptable tt
          INNER JOIN INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS ReferentialConstraint
             ON tt.FKConstraintName = ReferentialConstraint.CONSTRAINT_NAME

    UPDATE @temptable SET
       PKConstraintTableSchema  = TABLE_SCHEMA,
       PKConstraintTableName  = TABLE_NAME
    FROM @temptable tt
       INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS TableConstraints
          ON tt.PKConstraintName = TableConstraints.CONSTRAINT_NAME

    UPDATE @temptable SET
       PKConstraintColumnName = COLUMN_NAME
    FROM @temptable tt
       INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE KeyColumnUsage
          ON tt.PKConstraintName = KeyColumnUsage.CONSTRAINT_NAME


    --Now to drop constraint:
    SELECT
       '
       ALTER TABLE [' + FKConstraintTableSchema + '].[' + FKConstraintTableName + '] 
       DROP CONSTRAINT ' + FKConstraintName + '

       GO'
    FROM
       @temptable

    --Finally to add constraint:
    SELECT
       '
       ALTER TABLE [' + FKConstraintTableSchema + '].[' + FKConstraintTableName + '] 
       ADD CONSTRAINT ' + FKConstraintName + ' FOREIGN KEY(' + FKConstraintColumnName + ') REFERENCES [' + PKConstraintTableSchema + '].[' + PKConstraintTableName + '](' + PKConstraintColumnName + ')

       GO'
    FROM
       @temptable

    GO

Disable all indexes (including the pk, which will disable all fks), then reenable the pks.

DECLARE @sql AS NVARCHAR(max)=''
select @sql = @sql +
    'ALTER INDEX ALL ON [' + t.[name] + '] DISABLE;'+CHAR(13)
from  
    sys.tables t
where type='u'

select @sql = @sql +
    'ALTER INDEX ' + i.[name] + ' ON [' + t.[name] + '] REBUILD;'+CHAR(13)
from  
    sys.key_constraints i
join
    sys.tables t on i.parent_object_id=t.object_id
where
    i.type='PK'


exec dbo.sp_executesql @sql;
go

[Do your data load]

Then bring everything back to life...

DECLARE @sql AS NVARCHAR(max)=''
select @sql = @sql +
    'ALTER INDEX ALL ON [' + t.[name] + '] REBUILD;'+CHAR(13)
from  
    sys.tables t
where type='u'

exec dbo.sp_executesql @sql;
go

Use the built-in sp_msforeachtable stored procedure.

To disable all constraints:

EXEC sp_msforeachtable "ALTER TABLE ? NOCHECK CONSTRAINT ALL";

To enable all constraints:

EXEC sp_msforeachtable "ALTER TABLE ? WITH CHECK CHECK CONSTRAINT ALL";

To drop all the tables:

EXEC sp_msforeachtable "DROP TABLE ?";

There is a easy way to this.

-- Disable all the constraint in database
EXEC sp_msforeachtable 'ALTER TABLE ? NOCHECK CONSTRAINT all'

-- Enable all the constraint in database
EXEC sp_msforeachtable 'ALTER TABLE ? WITH CHECK CHECK CONSTRAINT all'

Reference SQL SERVER – Disable All the Foreign Key Constraint in Database – Enable All the Foreign Key Constraint in Database