SQL UNIQUE Constraint

constraint ensures that all values in a column are unique.

and

constraints provide a guarantee for uniqueness for a column or set of columns. However, you can have many

constraints per table, but only one

constraint per table.

constraint for the "ID" column upon creation of the "Persons" table:

( 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)

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)

constraint on the "ID" column when the table is already created, use the following SQL syntax:

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

constraint, use the following SQL: