Unique constraint oracle

A unique constraint is a single field or combination of fields that uniquely defines a record. Oracle unique constraint syntax. As long as the data set in the group of columns is unique , entry of null values is valid in this constraint.

A primary key constraint combines a NOT NULL constraint and a unique constraint in a single declaration. The UNIQUE constraint ensures that all values in a column are different.

Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint. Find out what fields have this constraint. You can have a number of unique constraints defined and the columns can have NULL values in them, unlike a column that belongs to a primary key constraint. This constraint helps in maintaining data integrity.

Unique Constraint What is it? It defines a field or set of fields where the combination must be unique in a table. So, if you create a unique constraint on one column, all of the values in that column must be unique.

Another option would be to modify the constraint so that it can allow duplicate values in your table. The first and universal method would be to manually adjust the constraint. You can also avoid rebuilding the index and eliminate redundant indexes by creating new primary key and unique constraints initially disabled. Then create (or use existing) nonunique indexes to enforce the constraint. How to create unique constraint on a column with duplicate values ,without disturbing the existing data.

To create a normal index first and then create a unique constraint. This has happened because the INSERT or UPDATE statement has created a duplicate value in a field that has either a PRIMARY KEY constraint or a UNIQUE constraint. Alternatively, you can define UNIQUE integrity constraints on the desired columns. Therefore, composite UNIQUE key constraints have the same limitations imposed on composite indexes: up to columns can constitute a composite unique key. When we create constraints in oracle , by default, the constraint exists in NON DEFERRABLE and VALIDATE state.

So, by default, oracle checks each time for unique data when we insert or update data. You can create constraint as DEFERRABLE and NOVALIDATE state. In the situation, oracle will not check existing duplicate data.

Unsubscribe from Tutorials Point (India) Pvt. UNIQUE Constraint enforces a column or set of columns to have unique values. Within a primary key constraint , at least one of the columns in the primary key for each row must be NOT NULL.

The primary key of a table is one of the candidate keys that you give some special characteristics.

Redundant indexes are also eliminated. For more information about PRIMARY KEY and UNIQUE constraints , see the ENABLE clause. Hi, Thanks for the solution. But I can neither do any changes in the existing data, nor drop the table.

If I use the normal index for my unique constraint , it is working but, since i need to put condition for that uniqueness, I need to make function based index only. UNIQUE constraints and CHECK constraints are two types of constraints that can be used to enforce data integrity in SQL Server tables. These are important database objects.

This topic contains the following sections. The downside is that this is an offline operation – the table is locked in Share mode. If there is more than one unique constraint , check in user_cons_columns to match the column to the constraint.