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2024年3月12日发(作者：java基础教程讲解)

oracle unique用法(一)

Oracle Unique

In this article, we will explore the various use cases

and detailed explanations of the “Oracle Unique” feature.

What is Oracle Unique?

Oracle Unique is a feature in the Oracle database that

ensures the uniqueness of values in a specified column or set

of columns within a table. It helps maintain data integrity

and prevents duplicates from being inserted into the table.

Use Cases

Here are some common use cases where Oracle Unique can be

beneficial:

• Primary Key Constraint: The primary key

constraint ensures that a specific column or combination

of columns in a table contains unique values. It helps

in uniquely identifying each row in the table.

• Unique Constraint: A unique constraint ensures

that the values in a specified column or combination of

columns are unique. Unlike a primary key constraint, a

unique constraint allows null values.

• Unique Index: A unique index is created on a

column or set of columns to improve the performance of

queries that require uniqueness. It enforces the

uniqueness of values in the indexed columns.

• Alternate Key Constraint: An alternate key

constraint ensures that a specific column or combination

of columns contains unique values, similar to a unique

constraint. However, an alternate key constraint may

allow null values.

• Foreign Key Constraint: A foreign key

constraint can reference a unique column or combination

of columns in another table. It ensures the referential

integrity by allowing only values that exist in the

referenced table.

How to Use Oracle Unique

To utilize the Oracle Unique feature, follow these steps:

1. Defining Unique Constraints:

– For a primary key constraint:

ALTER TABLE table_name

ADD CONSTRAINT constraint_name PRIMARY KEY(col

umn_name);

–

ame);

2.

Creating Unique Indexes:

CREATE UNIQUE INDEX index_name ON table_na

For a unique constraint:

ALTER TABLE table_name

ADD CONSTRAINT constraint_name UNIQUE(column_n

me(column_name);

3.

Defining Foreign Key Constraints:

ALTER TABLE child_table

ADD CONSTRAINT constraint_name FOREIGN KEY(column_n

ame)

REFERENCES parent_table(parent_column_name);

Conclusion

Oracle Unique offers a range of capabilities to enforce

uniqueness and maintain data integrity in the Oracle database.

By utilizing primary key constraints, unique constraints,

unique indexes, and foreign key constraints, developers can

design robust and reliable database schemas.


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