2011年6月24日
Defining Data Integrity
摘要： Primary Key Constraints:A primary key constraint enforces uniqueness of rows and also disallows NULLs in the constraint attributes.ALTER TABLE dbo.EmployeesADD CONSTRAINT PK_Employees PRIMARY KEY(empid);Unique Constraints:A unique constraint enforces uniqueness of rows, allowing you to implement the 阅读全文
posted @ 2011-06-24 17:10 HelloWorld.Michael 阅读(180) 评论(0) 推荐(0)