How to drop a list of SQL Server tables, ignoring constraints?

Question

I have a list of half a dozen MSSQL 2008 tables that I would like to remove at once from my database. The data has been entirely migrated to new tables. There is no reference in

Answer 1

I found a reasonable(ish) way to do it by making SQL write the SQL to drop the constraints:

select concat("alter table ", table_name, " drop ", constraint_type ," ", constraint_name, ";")
  from information_schema.table_constraints 
  where table_name like 'somefoo_%' 
        and 
        constraint_type <> "PRIMARY KEY";

You will want to modify the table name to suit your needs, or possibly select against other column/values.

Also, this would select any non primary key constraint, which might be too big of a sledgehammer. Maybe you need to just set it to =?

I am not a DBA. there may be better ways to do this, but it worked well enough for my purposes.

Answer 2

A simple DROP TABLE dbo.MyTable will ignore all constraints (and triggers) except foreign keys (unless you drop the child/referencing table first) where you may have to drop these first.

Edit: after comment:

There is no automatic way. You'll have to iterate through sys.foreign_keys and generate some ALTER TABLE statements.

Answer 3

I suspect that you would have to do an 'alter' command on the offending tables before the drop to remove the forigen key contraints.

ALTER TABLE Orders DROP FOREIGN KEY fk_PerOrders;
DROP TABLE Orders;

Of course if you drop the child tables first, then you wont have this problem. (unless you have table A contraint to table B and table B constraint to A, then you will need to Alter one of the tables, e.g. A to remove the constraint)

e.g. this WONT work, since Orders has a contraint from Order_Lines

DROP TABLE Orders;
DROP TABLE Order_lines;

e.g. this will work

DROP TABLE Order_lines;
DROP TABLE Orders;

Answer 4

It depends on how you want to drop the tables. If list of tables need to drop covers almost above 20 % of tables under your DB.

Then I will disable all the constraints in that DB under my script and drop the tables and Enable the constraints under the same script.

--To Disable a Constraint at DB level

EXEC sp_MSForEachTable 'ALTER TABLE ? NOCHECK CONSTRAINT ALL'

--Write the code to DROP tables

DROP TABLE TABLENAME

DROP TABLE TABLENAME

DROP TABLE TABLENAME

--To Enable a Constraint at DB level

EXEC sp_MSForEachTable 'ALTER TABLE ? CHECK CONSTRAINT ALL'

Finally to check the Status of your constraints fire up this Query.

--Checks the Status of Constraints

SELECT (CASE 
    WHEN OBJECTPROPERTY(CONSTID, 'CNSTISDISABLED') = 0 THEN 'ENABLED'
    ELSE 'DISABLED'
    END) AS STATUS,
    OBJECT_NAME(CONSTID) AS CONSTRAINT_NAME,
    OBJECT_NAME(FKEYID) AS TABLE_NAME,
    COL_NAME(FKEYID, FKEY) AS COLUMN_NAME,
    OBJECT_NAME(RKEYID) AS REFERENCED_TABLE_NAME,
    COL_NAME(RKEYID, RKEY) AS REFERENCED_COLUMN_NAME
FROM SYSFOREIGNKEYS
ORDER BY TABLE_NAME, CONSTRAINT_NAME,REFERENCED_TABLE_NAME, KEYNO

If you dont want to disable the constraints at Database level then make a list of tables which you want to drop.

Step1 : Check the Constraints associated with thos tables

SELECT * 
FROM sys.foreign_keys
WHERE referenced_object_id = object_id('dbo.Tablename')

Step2 : Disable the Constraints which are associated with these tables.

ALTER TABLE MyTable NOCHECK CONSTRAINT MyConstraint

Step3 : Drop the tables

DROP TABLE TABLENAME

Answer 5

Run the following script to delete all the constraints in all tables under current DB and then run the drop table statements.

DECLARE @dropAllConstraints NVARCHAR(MAX) = N'';

SELECT @dropAllConstraints  += N'
ALTER TABLE ' + QUOTENAME(OBJECT_SCHEMA_NAME(parent_object_id))
    + '.' + QUOTENAME(OBJECT_NAME(parent_object_id)) + 
    ' DROP CONSTRAINT ' + QUOTENAME(name) + ';'
FROM sys.foreign_keys;
EXEC sp_executesql @dropAllConstraints 

Answer 6

I finally found the solution based on the script provided by Jason Presley. This script automatically removes all constraints in the DB. It's easy to add a WHERE clause so that it only applies to the set of concerned tables. After that, dropping all tables is a straightforward.