SQL UNIQUE Keyword

❮ SQL Keywords

constraint ensures that all values in a column are unique.

The following SQL creates a UNIQUE constraint on the "ID" column when the "Persons" table is created:

( ID int NOT NULL UNIQUE, LastName varchar(255) NOT NULL, FirstName varchar(255),

( ID int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Age int, UNIQUE (ID)

To name a UNIQUE constraint, and to define a UNIQUE constraint on multiple columns, use the following SQL syntax:

( ID int NOT NULL, LastName varchar(255) NOT NULL, FirstName varchar(255), Age int, CONSTRAINT UC_Person UNIQUE (ID,LastName)

To create a UNIQUE constraint on the "ID" column when the table is already created, use the following SQL:

To name a UNIQUE constraint, and to define a UNIQUE constraint on multiple columns, use the following SQL syntax:

To drop a UNIQUE constraint, use the following SQL:

❮ SQL Keywords