W3Schools SQL | #45 SQL UNIQUE CONSTRAINT

SQL UNIQUE Constraint

SQL UNIQUE Constraint

열의 모든 값이 다르도록

SQL UNIQUE Constraint on CREATE TABLE

CREATE TABLE Persons (
    ID int NOT NULL UNIQUE, 
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int
);

SQL UNIQUE Constraint on ALTER TABLE

ALTER TABLE Persons
ADD UNIQUE (ID);

DROP a UNIQUE Constraint

ALTER TABLE Persons
DROP CONSTRAINT UC_Persons;