- A primary key can’t be created on a null able column wherein a unique key can be created on a null able column. - There can be only one primary key on a table wherein a table can have multiple unique key defined on it. Let’s create a table with a primary key and a unique...
id int not null auto_increment primary key, name varchar(16) not null )default charset=utf8; create table boy_girl( id int not null auto_increment primary key, boy_id int not null, girl_id int not null, constraint fk_boy foreign key boy_girl(boy_id) references boy(id), constraint ...
间隙锁GapLock:将记录之间的间隙锁住,间隙锁住了便可以解决幻读问题,只在RR隔离级别有效。 NextKeyLock:既想锁定一行,又想锁定行之间的记录,就是NextKey,即1和2的结合体。 1.3 加锁角度的锁 S锁:共享锁/读锁,S LOCK可以同时分发给多个TX,允许多个TX读取同一个Record X锁:排它锁/写锁,X LOCK不可以同时分...
SQL Server contains the NEWID() function. This function creates a unique value of type uniqueidentifier. We can use this function in several ways to generate unique numbers to suit our requirements : NEWID() generate alphanumeric value of 36 char. ...
You can create a unique constraint in SQL Server by using SQL Server Management Studio or Transact-SQL to ensure no duplicate values are entered in specific columns that don't participate in a primary key. Creating a unique constraint automatically creates a corresponding unique index. Note For ...
Represents the unique or primary key constraint. This class translates 80 syntax into 90 syntax, this should be reflected in the AST, if a differentiator is to be written.C# 複製 [System.Serializable] public class UniqueConstraintDefinition : Microsoft.SqlServer.TransactSql.ScriptDom...
A uniqueifier (or uniquifier as reported by SQL Server internal tools) is a 4-byte value used to make each key unique in a clustered index that allow duplicate key values. This uniqueness is required because each clustering key must point to exactly one record, without the uniqueifier a ...
标识数据库表中的每一条记录,即在单表中不能用每条记录是唯一的(例如身份证就是唯一的),Unique(要求列唯一)和Primary Key(primary key = unique + not null 列唯一)约束均为列或列集合中提供了唯一性的保证,Primary Key是拥有自动定义的Unique约束,但是每个表中可以有多个Unique约束,但是只能有一个Primary Key...
This topic describes how to create a unique index on a table in SQL Server by using SQL Server Management Studio or Transact-SQL. A unique index guarantees that the index key contains no duplicate values and therefore every row in the table is in some way unique. There are no significant ...
JoinUniqueKey Property 后续版本的 Microsoft SQL Server 将删除该功能。 请避免在新的开发工作中使用该功能,并着手修改当前还在使用该功能的应用程序。 The JoinUniqueKey property configures join clause interpretation for merge replication articles horizontally partitioned by criteria established in second articles...