How to use unique in oracle

The UNIQUE constraint in Oracle ensures that specific columns or column combinations in the table have unique values to prevent duplicate data insertion. It is implemented through the following rules: 1. In an insert or update operation, the value of a specified column or column combination cannot be repeated with an existing value; 2. Indexes are allowed to be created to improve query efficiency.

Usage of UNIQUE constraint in Oracle

UNIQUE constraint is a database constraint used to ensure that a certain A column or combination of columns with unique values. When you apply a UNIQUE constraint to a column, the database enforces the following rule:

• No duplicate values are allowed in that column or combination of columns.
• For an insert or update of the same row, if the value of the column or column combination conflicts with an existing row, the operation will fail.

Usage:

To define a UNIQUE constraint, you can use the following syntax:

ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column_list);

Where:

• table_nameis the name of the table to which the constraint applies.
• constraint_nameis the name of the constraint to be created.
• column_listis a list of columns or column combinations to be defined as unique.

Function:

UNIQUE constraints have the following functions:

• Maintain the integrity and uniqueness of the data.
• Prevent duplicate data from entering the table.
• Improve query efficiency because indexes can be built on columns with UNIQUE constraints.
• Helps identify and remove duplicate data.

Example:

To create a UNIQUE constraint for the "customer_id" column in the "Customers" table, you can use the following command:

ALTER TABLE Customers ADD CONSTRAINT customer_id_unique UNIQUE (customer_id);

Note:

UNIQUE constraints are different from PRIMARY KEY constraints. PRIMARY KEY constraints enforce uniqueness and non-null values, while UNIQUE constraints only enforce uniqueness.

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