oracle primary key delete

In Oracle database, the primary key is an important constraint to ensure that only unique records exist in each table. When it is necessary to delete a primary key, some care and steps are required to ensure data integrity and consistency.

Here are some steps to help you delete a primary key in Oracle database:

1. Check dependencies

Before deleting a primary key, you need to confirm the primary key Whether it is dependent on other objects. You can use the following script query:

SELECT constraint_name, table_name
FROM user_constraints
WHERE constraint_type = 'R'
  AND r_constraint_name = '<primary_key_name>'; 

If the query result contains one or more records, it indicates that the primary key may be dependent on a foreign key, and the foreign key associated with the primary key needs to be deleted first.

2. Delete foreign keys

Assuming that foreign key constraints that depend on the primary key are found, these foreign keys need to be deleted to delete the primary key. All related foreign key constraints can be queried using the following script:

SELECT constraint_name, table_name
FROM user_constraints
WHERE constraint_type = 'R'
  AND r_constraint_name = '<primary_key_name>'; 

For each foreign key constraint, they can be deleted using the following statement:

ALTER TABLE <table_name> DROP CONSTRAINT <foreign_key_name>; 

3. Cancel primary key

Once you confirm that no foreign keys depend on the primary key, you can execute the following script to cancel the primary key:

ALTER TABLE <table_name> DROP CONSTRAINT <primary_key_name>; 

Please note that after the primary key is deleted, it can no longer be used as a reference constraint for foreign keys. If you need to use this column as a foreign key, you need to recreate the primary key.

4. Re-create the primary key

If you need to re-create the primary key, you can use the following statement:

ALTER TABLE <table_name> ADD CONSTRAINT <primary_key_name> PRIMARY KEY (<column_name>); 

Please note that to ensure the uniqueness of the primary key, you cannot Insert duplicate values ​​for this column. If you need to correct the data before re-creating the primary key, you can use the following statement:

DELETE FROM <table_name>
WHERE rowid NOT IN (SELECT MIN(rowid)
                    FROM <table_name>
                    GROUP BY <column_name>);

This will remove duplicate records in the table to ensure that new primary keys can be added without triggering unique constraints.

In short, there may be some cautions and steps when deleting the primary key in the Oracle database, which requires vigilance and attention. This article gives some guidance on the steps to perform this process and provides some useful scripts and statements to help you perform the operation completely and accurately, ensuring data integrity and consistency.

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