SQL Server method for determining if a specific table constraint exists.

SQLServerTestForConstraint.sql

DECLARE @constraintName varchar(200);
SET @constraintName = 'SomeConstraintName';

IF (  SELECT count(*) FROM sys.objects 
      WHERE type_desc LIKE '%CONSTRAINT'
        AND OBJECT_NAME(object_id) = @constraintName) <> 0 BEGIN
  PRINT 'FOUND Constraint: ' + @constraintName;
  -- Perform some action...
  END
ELSE
  PRINT 'CANNOT FIND Constraint: ' + @constraintName;