Oracle PL/SQL constraints

An Oracle PL/SQL constraint is a rule that must be followed by the data in a database table. PL/SQL constraints can be used to enforce data integrity, prevent duplicate data, and ensure that data is valid.

Benefits of using PL/SQL constraints on a table include:

– Enforcing data integrity
– Preventing duplicate data
– Ensuring that data is valid

PL/SQL constraints can be added to a table in Oracle database using the following commands:
add primary key to a table, add constraint foreign key, drop constraint, enable and disable a foreign key.

Add primary key

ALTER TABLE table_name 
ADD CONSTRAINT constraint_name 
PRIMARY KEY (column_name);

Example how to Add primary key

Add foreign key

ALTER TABLE table_name 
ADD CONSTRAINT constraint_name 
FOREIGN KEY (column_name) 
REFERENCES table_name (column_name);

Example how to Add constraint foreign key

Drop constraint

ALTER TABLE table_name 
DROP CONSTRAINT constraint_name;

Example how to Drop constraint key

Enable a foreign key

ALTER TABLE table_name 
ENABLE CONSTRAINT constraint_name;

Example how to Enable a foreign key

Disable a foreign key

ALTER TABLE table_name 
DISABLE CONSTRAINT constraint_name;

Example how to Disable a foreign key

Constraints can also be used to check multiple conditions. For example, a unique constraint can be used to ensure that no two rows in a table have the same values for a certain column.

Oracle PL/SQL constraints are an important part of ensuring data integrity in a database. By using constraints, you can prevent duplicate data, ensure data is valid, and enforce data integrity.