增加约束键
ALTER TABLE Persons ADD UNIQUE (P_Id)
创建表时加入约束键
CREATE TABLE Persons
(
P_Id int NOT NULL,LastName varchar(255) NOT NULL,FirstName varchar(255),Address varchar(255),City varchar(255),UNIQUE (P_Id),UNIQUE (LastName)
)
ALTER TABLE Persons ADD UNIQUE (P_Id)
CREATE TABLE Persons
(
P_Id int NOT NULL,LastName varchar(255) NOT NULL,FirstName varchar(255),Address varchar(255),City varchar(255),UNIQUE (P_Id),UNIQUE (LastName)
)