id22intnotnull);altertabletest01addconstraintpk_id1primarykey(id1); 考虑如下关系 test02表中的id11依赖于test01中的id1,因此为test02创建外键 altertabletest02addconstraintfk_id11foreignkey(id11)referencestest01(id1); 注意:test01表中的id1必须为主键或者唯一索引,否则无法创建基于id1的外键。 创建外键...
主键约束 (Primary Key) 主键是表中的唯一标识符,用于确保每行数据的唯一性。 语法:`ADD CONSTRAINT PK_ColumnName PRIMARY KEY (ColumnName)` 外键约束 (Foreign Key) 外键用于建立两个表之间的关系,确保引用数据的完整性。 语法:`ADD CONSTRAINT FK_ForeignKeyName FOREIGN KEY (ForeignKeyColumn) REFERENCES Refer...
foreign key(Fid) references MainTable1(Fid) -- 添加多个约束(逗号隔开) alter table 表名 add constraint 约束名 约束类型与条件 …… --删除约束 alter table 表名 drop constraint 约束名 可以删除多个约束,用,分隔开
Like the primary key constraint, the unique constraint automatically creates a unique index with the same name as the constraint. By default, the index will be nonclustered. SQL uses that index to enforce the uniqueness of the column or combination of columns. 和主键约束一样,唯一性约束自动创建...
在关系型数据库中,外键约束(Foreign Key Constraint)是一种重要的数据完整性机制。它用于维护两个表之间的参照完整性,确保一个表中的值在另一个表中存在,从而防止孤立记录和无效数据的插入。以下是如何在SQL中定义和使用外键约束的详细指南。 1. 创建表时添加外键约束 在创建表的同时,可以直接使用FOREIGN KEY子句来...
30)NOTNULL,DeptIdchar(2)NOTNULL,ClassStuNumberint)---CREATETABLETb_Class(ClassIdchar(8)NOTNULL,ClassNamevarchar(30)NOTNULL,DeptIdchar(2)NOTNULL,ClassStuNumberint,CONSTRAINTPK_ClassIdPRIMARYKEY(ClassId,ClassName))2020/3/1 ---江阴职业技术学院计算机系--- MicrosoftSQLServer2005 4 ...
FeatureFOREIGN KEYApplies to:Azure SQL Database and SQL Server starting SQL Server 2016 (13.x) For memory-optimized tables, FOREIGN KEY constraints are only supported for foreign keys referencing primary keys of other memory-optimized tables. Remove the constraint from the table definition if the ...
Feature FOREIGN KEY Applies to: Azure SQL Database and SQL Server starting SQL Server 2016 (13.x)For memory-optimized tables, FOREIGN KEY constraints are only supported for foreign keys referencing primary keys of other memory-optimized tables. Remove the constraint from the table definition if th...
Feature FOREIGN KEY Applies to: Azure SQL Database and SQL Server starting SQL Server 2016 (13.x)For memory-optimized tables, FOREIGN KEY constraints are only supported for foreign keys referencing primary keys of other memory-optimized tables. Remove the constraint from the table definition if th...
A statement that adds a foreign key constraint : Foreign Key « Constraints « SQL Server / T-SQL Tutorial ALTER TABLE YourTableName WITH CHECK ADD FOREIGN KEY (AccountNo) REFERENCES AnotherTableName(AccountNo)