Learn about primary and foreign key constraints, important objects used to enforce data integrity in database tables.
如需命名 FOREIGN KEY 约束,并定义多个列的 FOREIGN KEY 约束,请使用下面的 SQL 语法: MySQL / SQL Server / Oracle / MS Access: CREATE TABLE Orders ( O_Id int NOT NULL, OrderNo int NOT NULL, P_Id int, PRIMARY KEY (O_Id), CONSTRAINT fk_PerOrders FOREIGN KEY (P_Id) REFERENCES Persons...
CONSTRAINT FOREIGN KEY(s_c_id) REFERENCES t_class(class_id); 1. 2. 3. 4. 5. 6. 7. 8. 9. 红色标识的就是创建外键约束的方法,个人认为也是SQL语句中最难记的。
-- 父表中引用的列名称tr.nameASReferencedTable,-- 被引用的表的名称cr.nameASReferencedColumn-- 被引用表中的列名称FROMsys.foreign_keysASfkINNERJOINsys.foreign_key_columnsASfkcONfk.object_id=fkc.constraint_object_idINNERJOINsys.tablesAStpONfkc.parent_object_id=tp.object_idINNER...
alter table 数据库名.[dbo].表名 with check add constraint 约束名 foreign key(列名) references 数据库名.[dbo].表名(列名) on delete cascade on update cascade; go 示例: if exists(select * from sysobjects where name='t1_t2') alter table [testss].[dbo].[test1] drop constraint t1_t2; ...
Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) Warehouse in Microsoft Fabric SQL database in Microsoft Fabric Contains a row per object that is a FOREIGN KEY constraint, with sys.object.type = ...
CONSTRAINT 外键名 FOREIGN KEY (字段1) REFERENCES 外表(字段1))举例说明：UNIQUE约束唯一标识数据库表中的每条记录。Persons表 以下SQL 在创建"Orders"表时在"PersonID"列上创建了一个FOREIGN KEY：CREATE TABLE Orders (OrderID int NOT NULL PRIMARY KEY,OrderNumber int NOT NULL,PersonID int FOREIGN KEY ...
https://blog.csdn.net/dengguawei0519/article/details/101315699 1。找到引用这个表外键名称 SELECT * FROM sys.foreign_keys WHERE referenced_object_id=OBJECT_ID('User'); 删除外键 删除掉引用表的外键 ALTER TABLE dbo.XX DROP constraint FK_User_XX...
also permits fast access to data when the primary key is used in queries. If a primary key constraint is defined on more than one column, values can be duplicated within one column, but each combination of values from all the columns in the primary key constraint definition must be unique....
SQL FOREIGN KEY on ALTER TABLE To create aFOREIGN KEYconstraint on the "PersonID" column when the "Orders" table is already created, use the following SQL: MySQL / SQL Server / Oracle / MS Access: ALTERTABLEOrders ADDFOREIGNKEY(PersonID)REFERENCESPersons(PersonID); ...