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

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

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

IF (OBJECT_ID('FK_ConstraintName', 'F') IS NOT NULL)
BEGIN
    ALTER TABLE dbo.TableName DROP CONSTRAINT FK_ConstraintName
END

C = CHECK constraint
D = DEFAULT (constraint or stand-alone)
F = FOREIGN KEY constraint
PK = PRIMARY KEY constraint
UQ = UNIQUE constraint

AF = Aggregate function (CLR)
C = CHECK constraint
D = DEFAULT (constraint or stand-alone)
F = FOREIGN KEY constraint
FN = SQL scalar function
FS = Assembly (CLR) scalar-function
FT = Assembly (CLR) table-valued function
IF = SQL inline table-valued function
IT = Internal table
P = SQL Stored Procedure
PC = Assembly (CLR) stored-procedure
PG = Plan guide
PK = PRIMARY KEY constraint
R = Rule (old-style, stand-alone)
RF = Replication-filter-procedure
S = System base table
SN = Synonym
SO = Sequence object

SQ = Service queue
TA = Assembly (CLR) DML trigger
TF = SQL table-valued-function
TR = SQL DML trigger
TT = Table type
U = Table (user-defined)
UQ = UNIQUE constraint
V = View
X = Extended stored procedure

create function fnGetForeignKeyName
(
    @ParentTableName nvarchar(255),
    @ParentColumnName nvarchar(255),
    @ReferencedTableName nvarchar(255),
    @ReferencedColumnName nvarchar(255)
)
returns nvarchar(255)
as
begin
    declare @name nvarchar(255)

    select @name = fk.name  from sys.foreign_key_columns fc
    join sys.columns pc on pc.column_id = parent_column_id and parent_object_id = pc.object_id
    join sys.columns rc on rc.column_id = referenced_column_id and referenced_object_id = rc.object_id
    join sys.objects po on po.object_id = pc.object_id
    join sys.objects ro on ro.object_id = rc.object_id
    join sys.foreign_keys fk on fk.object_id = fc.constraint_object_id
    where
        po.object_id = object_id(@ParentTableName) and
        ro.object_id = object_id(@ReferencedTableName) and
        pc.name = @ParentColumnName and
        rc.name = @ReferencedColumnName

    return @name
end

go

declare @name nvarchar(255)
declare @sql nvarchar(4000)
-- hunt for the constraint name on 'Badges.BadgeReasonTypeId' table refs the 'BadgeReasonTypes.Id'
select @name = dbo.fnGetForeignKeyName('dbo.Badges', 'BadgeReasonTypeId', 'dbo.BadgeReasonTypes', 'Id')
-- if we find it, the name will not be null
if @name is not null
begin
    set @sql = 'alter table Badges drop constraint ' + replace(@name,']', ']]')
    exec (@sql)
end

ALTER TABLE [dbo].[TableName]
    DROP CONSTRAINT FK_TableName_TableName2

IF (OBJECT_ID('DF_Constraint') IS NOT NULL)
BEGIN
    ALTER TABLE [dbo].[tableName]
    DROP CONSTRAINT DF_Constraint
END

Declare @FKeyRemoveQuery NVarchar(max)

IF EXISTS(SELECT 1 FROM sys.foreign_keys WHERE parent_object_id = OBJECT_ID(N'dbo.TableName'))

BEGIN
    SELECT @FKeyRemoveQuery='ALTER TABLE dbo.TableName DROP CONSTRAINT [' + LTRIM(RTRIM([name])) + ']'
    FROM sys.foreign_keys
    WHERE parent_object_id = OBJECT_ID(N'dbo.TableName')

    EXECUTE Sp_executesql @FKeyRemoveQuery

END

DECLARE @ConstraintName nvarchar(200)
SELECT
    @ConstraintName = KCU.CONSTRAINT_NAME
FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS AS RC
INNER JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS KCU
    ON KCU.CONSTRAINT_CATALOG = RC.CONSTRAINT_CATALOG
    AND KCU.CONSTRAINT_SCHEMA = RC.CONSTRAINT_SCHEMA
    AND KCU.CONSTRAINT_NAME = RC.CONSTRAINT_NAME
WHERE
    KCU.TABLE_NAME = 'TABLE_NAME' AND
    KCU.COLUMN_NAME = 'TABLE_COLUMN_NAME'
IF @ConstraintName IS NOT NULL EXEC('alter table TABLE_NAME drop  CONSTRAINT ' + @ConstraintName)