Question

I can drop a table if it exists using the following code but do not know how to do the same with a constraint:

IF EXISTS(SELECT 1 FROM sys.objects WHERE OBJECT_ID = OBJECT_ID(N'TableName') AND type = (N'U')) DROP TABLE TableName go  

I also add the constraint using this code:

ALTER TABLE [dbo].[TableName]    WITH CHECK ADD CONSTRAINT [FK_TableName_TableName2] FOREIGN KEY([FK_Name])     REFERENCES [dbo].[TableName2] ([ID]) go 

Answer 1

The more simple solution is provided in Eric Isaacs’s answer. However, it will find constraints on any table. If you want to target a foreign key constraint on a specific table, use this:

IF EXISTS (SELECT *    FROM sys.foreign_keys     WHERE object_id = OBJECT_ID(N'FK_TableName_TableName2')    AND parent_object_id = OBJECT_ID(N'dbo.TableName') )   ALTER TABLE [dbo].[TableName] DROP CONSTRAINT [FK_TableName_TableName2]