然后在如下语句中添加或修改 ON DELETE ... 部分到 ON DELETE CASCADE (保留其他所有内容): ALTER TABLE kontakty DROP CONSTRAINT kontakty_ibfk_1 , ADD CONSTRAINT kontakty_ibfk_1 FOREIGN KEY (id_osoby) REFERENCES osoby (id_osoby) ON DELETE CASCADE; 没有ALTER CONSTRAINT 命令。在单个 ALTER TABLE ...
如果删除B表中的记录,则会级联删除A表中对应记录 createtabletest(id serialprimarykey, namevarchar(10)); createtabletest01(id serialprimarykey, tidint,constraintfk_test01_tidforeignkey(tid)referencestest(id)ondeletecascade); imos=#insertintotest(name)values('a'),('b'),('c');INSERT03imos=#ins...
三、外键行为配置 级联操作(CASCADE) 合理配置ON DELETE和ON UPDATE规则,避免手动维护关联数据。例如,级联删除用户时自动清理订单: CREATE TABLE orders ( ... FOREIGN KEY (user_id) REFERENCES users(user_id) ON DELETE CASCADE ); 1. 2. 3. 4. 指出级联操作可简化代码,但需评估业务风险。 延迟约束检查 ...
外键名 FOREIGN KEY(副表的外键字段) REFERENCES 主表(主表的主键) -- 部门表(主表) CREATE TABLE T_Department( Id INT PRIMARY KEY...DELETE CASCADE 注意: 级联操作必须在外键基础上使用 CREATE TABLE T_Employee( Id INT PRIMARY KEY AUTO_INCREMENT, NAME... ON DELETE CASCADE ) 3、数据库三大范式...
postgresql外键on delete cascade 级联删除 A表中字段依赖于B表中对应字段, 如果删除B表中的记录,则会级联删除A表中对应记录 create table test(id serial primary key, name varchar(10)); 1. create table test01(id serial primary key, tid int, constraint fk_test01_tid foreign key(tid) references ...
DETAIL:Key(a, b)=(1,1)isstill referencedfromtable"tbl_foreign". 测试例2.match full on delete cascade on update cascade 删除外键约束,清空数据,重新增加外键 test=#altertabletbl_foreigndropconstraintfk_tbl_foreign_a_b ;ALTERTABLEtest=#deletefromtbl_foreign;DELETE4test=#altertabletbl_foreignaddcon...
Third, delete a department and observe the cascading effect on associated employees: DELETE FROM departments WHERE id = 1; Once you execute this statement, it deletes all employees belonging to the department with department_id = 1 due to the DELETE CASCADE action defined on the foreign key co...
SQL 标准定义了 6 种完整性约束:非空约束(NOT NULL)、唯一约束(UNIQUE)、主键约束(Primary Key)、外键约束(Foreign Key)、检查约束(CHECK)以及默认值。 MySQL(InnoDB 和 NDB)支持了完整的约束,PostgreSQL 则提供了更多的约束选项。 功能特性MySQLPostgreSQL 非空约束 ✔️ ✔️ 唯一约束 ✔️ ✔️...
1. Missing CASCADE Clause:Attempting to delete a parent row without the CASCADE clause in the foreign key will result in an error: ERROR: update or delete on table "authors" violates foreign key constraint 2. Unintended Deletions:Cascading deletions can lead to loss of important data if not ...
DELETE 删除一个表中的行。 DELETE FROM [ ONLY ] table [ WHERE condition ] DROP AGGREGATE 删除一个用户定义的聚集函数。 DROP AGGREGATE name ( type ) [ CASCADE | RESTRICT ] DROP CAST 删除一个用户定义的类型转换。 DROP CAST (source_type AS target_type) [ CASCADE | RESTRICT ] ...