Hey guys,
Good morning!

Introduction

In this post I will demonstrate to you how to identify, delete and recreate Foreign Keys (FK) of a table in SQL Server. Many times we need to delete a table or just change a column, but the database sends us an error message informing us that there is a foreign key constraint for that column, making it impossible for the DBA to make the requested change.

Msg 5074, Level 16, State 1, Line 57
The object ‘PK__Clientes__3214EC07F3BD01EC’ is dependent on column ‘Id’.
Msg 5074, Level 16, State 1, Line 57
The object ‘FK_Cliente_Telefone’ is dependent on column ‘Id’.
Msg 5074, Level 16, State 1, Line 57
The object ‘FK_Cliente_Endereco’ is dependent on column ‘Id’.
Msg 4922, Level 16, State 9, Line 57
ALTER TABLE ALTER COLUMN Id failed because one or more objects access this column.

To resolve this problem, you must remove the FK contraints, make the change to the table and then create it again. When the table has many references, this task becomes a bit laborious, especially if several tables are involved.

To facilitate this activity, which is very common in everyday life, I decided to create and make available to you, a Stored Procedure that checks the FK's in the SQL Server catalog views and brings the complete list.

Important: Due to technical restrictions, SQL Server allows you to create Foreign Keys only between objects in the same database.

Creating the test mass

To demonstrate the use of this procedure, I created this simple script so that you can generate a mass of tests and test the SP.

IF (OBJECT_ID('dbo.Clientes') IS NOT NULL) DROP TABLE dbo.Clientes
CREATE TABLE dbo.Clientes (
    Id INT IDENTITY(1,1) PRIMARY KEY,
    Nome VARCHAR(50)
)

INSERT INTO dbo.Clientes
SELECT 'Dirceu'
UNION ALL
SELECT 'Patricia'
UNION ALL
SELECT 'Lucas'
UNION ALL
SELECT 'Leandro'
UNION ALL
SELECT 'Richardson'


IF (OBJECT_ID('dbo.Enderecos') IS NOT NULL) DROP TABLE dbo.Enderecos
CREATE TABLE dbo.Enderecos (
    Id INT IDENTITY(1,1) PRIMARY KEY,
    Id_Cliente INT,
    Ds_Endereco VARCHAR(50)
)

ALTER TABLE dbo.Enderecos ADD CONSTRAINT FK_Cliente_Endereco FOREIGN KEY (Id_Cliente) REFERENCES dbo.Clientes(Id)


INSERT INTO dbo.Enderecos (Id_Cliente, Ds_Endereco)
SELECT 1, 'Endereço Teste Cliente 1'
UNION ALL
SELECT 2, 'Endereço Teste Cliente 2'
UNION ALL
SELECT 3, 'Endereço Teste Cliente 3'
        



IF (OBJECT_ID('tempdb..dbo.Telefones') IS NOT NULL) DROP TABLE dbo.Telefones
CREATE TABLE dbo.Telefones (
    Id INT IDENTITY(1,1) PRIMARY KEY,
    Id_Cliente INT,
    Nr_Telefone VARCHAR(11)
)

ALTER TABLE dbo.Telefones ADD CONSTRAINT FK_Cliente_Telefone FOREIGN KEY (Id_Cliente) REFERENCES dbo.Clientes(Id)


INSERT INTO dbo.Telefones (Id_Cliente, Nr_Telefone)
SELECT 1, '27999998888'
UNION ALL
SELECT 4, '27999997777'
UNION ALL
SELECT 5, '27999996666'


IF (OBJECT_ID('dbo.Teste1') IS NOT NULL) DROP TABLE dbo.Teste1
CREATE TABLE dbo.Teste1 (
    Cod1 INT NOT NULL,
    Cod2 int NOT NULL,
    Cod3 int NOT NULL,
    Nome VARCHAR(200)
)

IF (OBJECT_ID('dbo.Teste2') IS NOT NULL) DROP TABLE dbo.Teste2
CREATE TABLE dbo.Teste2 (
    Codigo1 INT NOT NULL,
    Codigo2 int NOT NULL,
    Codigo3 int NOT NULL,
    Nome VARCHAR(200)
)

ALTER TABLE dbo.Teste2 ADD CONSTRAINT [PK_Teste2] PRIMARY KEY (Codigo1, Codigo2, Codigo3)
ALTER TABLE dbo.Teste1 ADD CONSTRAINT [FK_Teste1] FOREIGN KEY (Cod1, Cod2, Cod3) REFERENCES dbo.Teste2(Codigo1, Codigo2, Codigo3)