The syntax for creating a foreign key with cascade delete in an ALTER TABLE statement in Oracle/PLSQL is: ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGN KEY (column1, column2, ... column_n) REFER
The syntax for creating a foreign key with cascade delete using a CREATE TABLE statement in SQL Server (Transact-SQL) is: CREATE TABLE child_table ( column1 datatype [ NULL | NOT NULL ], column2 datatype [ NULL | NOT NULL ], ... CONSTRAINT fk_name FOREIGN KEY (child_col1, child_...
SQLForeignKeys以标准结果集的形式返回结果。 如果请求与主键关联的外键,则按FKTABLE_CAT、FKTABLE_SCHEM、FKTABLE_NAME和KEY_SEQ对结果集进行排序。 如果请求与外键关联的主键,则按PKTABLE_CAT、PKTABLE_SCHEM、PKTABLE_NAME和KEY_SEQ对结果集进行排序。 下表列出了结果集中的列。
Syntax: Foreign Key Copy CONSTRAINT <foreignkey_name> FOREIGN KEY (<column_name>) REFERENCES <reference_tablename> (<column_name>) [ON DELETE CASCADE] [ON UPDATE CASCADE]In the above syntax, <foreignkey_name> is the name of a foreign key that should be in the FK_TableName_ReferenceTable...
mysql 使用foreign key(外键) 插入约束 实验: //创建父表,并添加索引 CREATE TABLE parent(id INT,msg VARCHAR(200), INDEX index_id(id)); //查看索引 SHOW INDEX FROM parent; //创建子表(外键) CREATE TABLE child (c_id INT,c_mgs VARCHAR(200),FOREIGN KEY (c_id) REFERENC... ...
适用于:SQL Server Azure SQL 数据库 Azure SQL 托管实例 Azure Synapse Analytics Analytics Platform System (PDW) SQL Server 支持通过外键约束机制进行级联更新和删除。 如果对 FOREIGN KEY 约束的 ON UPDATE 和/或 ON DELETE 子句指定 CASCADE 选项,则 SQL Server 将返回UPDATE_RULE和/或DELETE_RULE列的SQL_...
Foreign keys do not have to be linked specifically to a primary key constraint in another table; they can also reference the columns of a UNIQUE constraint elsewhere. Foreign key constrains are not the only types of constraints. The following are some other SQL constraint types: ...
ALTER TABLE tbl_name DROP FOREIGN KEY foreign_key_name; SQL Copy Example ALTER TABLE teacher DROP FOREIGN KEY teacher_ibfk_1; SQL Copy After dropping the foreign key link with the master table, add this foreign in your child table with constraints like delete cascade. Right-click on your ch...
[PRIMARY KEY]用于指定表的主键(即关系中的主属性),实体完整性约束条件规定:主键必须是唯一的,非空的; [,FOREIGN KEY (列名[,列名]...) REFERENCE<表名>(列名[,列名]...)]是用于指定外键参照完整性约束条件,FOREIGN KEY指定相关列为外键,其参照对象为另外一个表的指定列,即使用REFERENCE引入的外表中的列...
A self-referential ON DELETE SET NULL, on the other hand, is possible, as is a self-referential ON DELETE CASCADE. Cascading operations may not be nested more than 15 levels deep. In an SQL statement that inserts, deletes, or updates many rows, foreign key constraints (like unique ...