In relational database design, the concepts of Primary Key and Unique Key are crucial for ensuring data integrity and establishing the relationships between tables. Although they may seem similar, they have distinct roles and characteristics. This article will explain the differences between the Primary...
2. The unique key is represented using a unique constraint while a primary key is created using a primary key constraint in any table and it's automatically got a unique constraint. You can also see these Database and SQL courses from Udemy and from Pluralsight for more details on how uniq...
the difference between primary key and unique key primary key:主键约束 unique key:唯一键约束 相同点:唯一,既值都不能重复 不同点: 1.一个表中只能有一个主键约束,但是唯一键约束可以有多个; 2.主键约束可以由一个或多个键组成,而唯一键约束只作用在一个键上; 3.主键作用的字段值不能为空,而唯一键作...
Unique: unique it allows null value only once. Primary key: It is unique but it does't allow null value. 0 Feb, 2011 3 in simple words...primary key is always unique and not null.but unique key is only unique it can be null. 0 Oct, 2010 12 From Microsoft SQL serv...
c# and SQL interview question Video :- What is the difference between unique key and primary key? Unique key can have nulls Primary key cannot have nulls. In a single table we can create multiple unique keys.In a single table we can have only one primary key....
Primary and Unique Key both enforce uniqueness of columns on which they are defined. Then where do they differ? They differ in following way - A primary key doesn’t allow null value wherein a unique key allows one null value. - A primary keys purpose is to uniquely define a row in a...
create unique clustered index index1 on #temp(id) as opposed to ALTER TABLE #temp ADD CONSTRAINT [PK_Individual_CustomerID] PRIMARY KEY CLUSTERED ( id ASC ) For a load table, I think you are safe with either approach. The difference is when there are relationships cr...
Before getting started, let me briefly describe SQL Server unique indexes vs. unique constraints: A unique index ensures that the values in the index key columns are unique. A unique constraint also guarantees that no duplicate values can be inserted into the column(s) on which the constrain...
• primary key (字段1,字段2...):联合主键索引 • unique(字段1,字段2..):联合唯一索引 • index(字段1,字段2..):联合普通索引 1. 2. 3. 应用场景 • 编号:int • 姓名:varchar(255) • 身份号:char(18) • 电话:char(11) ...
What is the basic difference between primary key and (unique key along with Not NULL). If we define a unique key as not null then it also take a unique value as well as not null value that means one can not insert Null value in that column. Thanks Was this answer useful? Yes ...