[SQL]SQL语句之添加主键和增加字段

记下来备用：

添加外键:

CREATE TABLE UserInfo(UserId INT NOT NULL PRIMARY KEY,[Password] NVARCHAR(20) NOT NULL,[UserName] NVARCHAR(20) NOT NULL)CREATE TABLE Friends(MainId INT NOT NULL,SubId INT NOT NULL)ALTER TABLE Friends ADD CONSTRAINT PK_Friends_MainId_UserInfo_Userid FOREIGN KEY(MainId) REFERENCES UserInfo(UserId)ALTER TABLE Friends ADD CONSTRAINT PK_Friends_SubId_UserInfo_Userid FOREIGN KEY(SubId) REFERENCES UserInfo(UserId)

添加字段:

ALTER TABLE Friends ADD testmemo varchar(200) NULL