Finding and Managing Oracle Constraints（oracle查找约束）

An Oracle constraint is a set of rules defined on a table column or a combination of table columns to maintain the integrity and accuracy of the data in a database table. Oracle constraints help to maintain data consistency, integrity and accuracy within a table. It enforces business rules and helps prevent invalid or unauthorized data from being stored in the table.

To find Oracle constraints, the user can query the data dictionary tables. The most commonly used data dictionary views for Oracle constraints are: USER_CONSTRAINTS, USER_TABCONSTRAINTS and ALL_CONSTRAINTS. Using these tables, one can:

• Get information on a specific constraint

• Get information on all the constraints in the database

• List all the tables with constraints.

In order to manage Oracle constraints, there are two main operations: creation and modification of constraints. To create a constraint, the user must have direct access to the Oracle database. The syntax for creating constraints is as follows:

CREATE [CONSTRAINT constraint_name]

TYPE {CHECK | FOREIGN KEY | NOT NULL | UNIQUE | PRIMARY KEY}

CHECK (condition)

ON table_name;

To modify an existing Oracle constraint, the user must use the ALTER TABLE command. The syntax for the command is as follows:

ALTER TABLE table_name

MODIFY constraint_name {CHECK | FOREIGN KEY | NOT NULL | UNIQUE | PRIMARY KEY} (condition);

Additionally, Oracle provides a “drop constraint” command, which is used to delete a constraint from the database. The syntax for the command is:

ALTER TABLE table_name

DROP CONSTRAINT constraint_name;

In conclusion, Oracle constraints are important for maintaining the accuracy and integrity of data in the database. To find or manage them, the user must have direct access to the Oracle database, which is accomplished by running queries on the Oracle data dictionary tables. Additionally, to create or modify constraints, the user must use ALTER TABLE commands. Overall, understanding Oracle constraints and being able to use the various management commands is essential for anyone aiming to have a successful Oracle database.