Converting Foreign Key Constraints Between SQL Server and Oracle

In this article, we will explore the process of converting a foreign key constraint from SQL Server to Oracle. We will cover the differences in syntax and behavior between these two databases and provide examples to illustrate the steps involved.

Understanding Foreign Key Constraints

A foreign key constraint is a mechanism used to establish relationships between tables in a database. It ensures that the values in a column of one table match the values in a related column of another table, thus maintaining data consistency.

In SQL Server, foreign key constraints can be created using the ALTER TABLE statement with the ADD CONSTRAINT option. For example:

ALTER TABLE [dbo].[TDistribucion]  WITH CHECK ADD  CONSTRAINT [FK_TDistribucion_TDocumentos] FOREIGN KEY([Id_Documento])
REFERENCES [dbo].[TDocumentos] ([Id])
GO
ALTER TABLE [dbo].[TDistribucion] CHECK CONSTRAINT [FK_TDistribucion_TDocumentos]
GO

In contrast, Oracle requires a different syntax for creating foreign key constraints. For example:

ALTER TABLE TDISTRIBUCION  WITH CHECK ADD CONSTRAINT FK_TDistribucion_TDocumentos FOREIGN KEY(ID_DOCUMENTO)
REFERENCES TDOCUMENTOS (ID);

The Problem with WITH CHECK ADD

The original query attempts to convert the SQL Server syntax to Oracle using WITH CHECK ADD. However, this approach is incorrect and results in an error message.

In Oracle, the ENABLE NOVALIDATE option cannot be used to create a foreign key constraint. Instead, you must use the ENABLE option to specify whether the constraint should be enabled or disabled.

Creating a Master Table

To create a master table with a primary key column, we can use the following SQL statement:

CREATE TABLE TDOCUMENTOS (
  ID NUMBER PRIMARY KEY
);

This statement creates a new table called TDOCUMENTOS with a single column named ID, which has a data type of NUMBER. The ID column is designated as the primary key using the PRIMARY KEY clause.

Creating a Detail Table

To create a detail table that references the master table, we can use the following SQL statement:

CREATE TABLE TDISTRIBUCION (
  ID NUMBER
);

This statement creates a new table called TDISTRIBUCION with a single column named ID, which has a data type of NUMBER. The ID column does not have any constraints or relationships to other tables.

Creating a Foreign Key Constraint

To create a foreign key constraint that references the master table, we can use the following SQL statement:

ALTER TABLE TDISTRIBUCION ADD CONSTRAINT FK_TDistribucion_TDocumentos FOREIGN KEY (ID)
REFERENCES TDOCUMENTOS (ID);

This statement creates a new constraint called FK_TDistribucion_TDocumentos and specifies that it should reference the ID column in both the TDISTRIBUCION table and the TDOCUMENTOS table.

Enabling the Foreign Key Constraint

To enable the foreign key constraint, we can use the following SQL statement:

ALTER TABLE TDISTRIBUCION ENABLE FOREIGN KEY (ID);

This statement enables the foreign key constraint specified in the previous step.

Checking for Validity

To check if the foreign key constraint is valid, you can use the following SQL statement:

SELECT * FROM TDOCUMENTOS;

SELECT * FROM TDISTRIBUCION;

These statements retrieve the data from both tables and display it in the output.

Inserting Data

To insert data into both tables, you can use the following SQL statements:

INSERT INTO TDOCUMENTOS (ID) VALUES (100);

INSERT INTO TDISTRIBUCION (ID) VALUES (100);

These statements insert a new row with ID value of 100 into both tables.

Violating the Foreign Key Constraint

To demonstrate that the foreign key constraint is enforced, we can try inserting data that violates it:

INSERT INTO TDOCUMENTOS (ID) VALUES (300);

INSERT INTO TDISTRIBUCION (ID) VALUES (400);

These statements attempt to insert a new row with ID value of 300 into the TDOCUMENTOS table, which has no matching rows. Similarly, they attempt to insert a new row with ID value of 400 into the TDISTRIBUCION table, which does not have a matching row in the TDOCUMENTOS table.

Conclusion

In this article, we explored the process of converting a foreign key constraint from SQL Server to Oracle. We covered the differences in syntax and behavior between these two databases and provided examples to illustrate the steps involved. By following these steps, you can create a reliable and consistent data model that enforces referential integrity between tables.

Last modified on 2024-07-27