One or more columns whose values are unique for all rows in a table.

a value that identifies each record (tuple) in a table and distinguishes it from other records. Therefore, one value of a unique key is used only by one record. The simplest type of unique key is a field whose values cannot be repeated, like an employee identity inside a company. Often, one single field doesn't suffice for creating unique values, so a combination of fields must be used. If this still doesn't suffice, then a surrogate key is used. In IB, when you declare an UK, the underlying index is created automatically and it always is in ascending order.

a good candidate for such a field, although the uniqueness of this field is not required

a key for which no two values are equal

a key that is constrained so that no two of its values are equal

a set of columns where no two values are duplicated in any other row

A field or index that uniquely identifies a record. This could be a system generated number.

A unique key is defined to have no two of its values the same. The columns of a unique key cannot contain null values. The constraint is enforced by the database manager during the execution of INSERT and UPDATE statements. A table can have multiple unique keys. Unique keys are optional and can be defined in CREATE TABLE or ALTER TABLE statements.

Is used to uniquely identify each record in an Oracle table. There can be one and only one row with each unique key value.

1- Defines the attributes and relationships that uniquely identify the entity. 2- A column or columns containing unique values for the rows of a table. A column in a Unique Key may contain a null. Therefore, a Unique Key defined for an entity may not make a suitable Primary for a table.

One or more columns that are unique in each row of a table. A unique key can be used as a primary key.

See primary key.

Unique Keys are used to uniquely identify each row in an Oracle table. There can be one and only one row for each unique key value.

In database design, a unique key refers to the set of columns which have a unique set of values for each row of the table. No two distinct rows in a table can have the same values in those columns.