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 ...
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 在事务结束时统一检查外键约束,而非每次操作时检查: ALTER TABLE orders ADD CONSTRAINT fk_user FOREIGN KEY (user_id) REFERENCES users(user_id) DEFERRABLE ...
alter table emp add constraint jfkdsj foreign key (did) references dept (id) ---例子 *2.数据库中delete和truncate的区别 (1)TRUNCATE TABLE比DELETE的速度快; (2)TRUNCATE table 是删除表的所有行,而DELETE是删除表的一行或者多行(除非DELETE不带WHERE语句); (3)在删除时如果遇到任何一行违反约束(主要是...
PostgreSQL foreign key constraint syntax The following illustrates a foreign key constraint syntax: [CONSTRAINT fk_name] FOREIGN KEY(fk_columns) REFERENCES parent_table(parent_key_columns) [ON DELETE delete_action] [ON UPDATE update_action] In this syntax: First, specify the name for the foreign...
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...
insert or update on table "orders" violates foreign key constraint "orders_product_no_fkey" 删除一个被引用的产品,如下: delete from products where product_no = 1; 提示错误如下: update or delete on table "products" violates foreign key constraint "orders_product_no_fkey" on table "orders" 先...
1ALTERTABLEt_permissionADDCONSTRAINTfkeyFOREIGNKEY(fd_resid)REFERENCESt_resource (fd_resid)ONDELETECASCADE;2ALTERTABLEt_permissionDROPCONSTRAINTfkey; 2.更新或删除的时候 1NO ACTION2如果违反外键约束会产生一个错误。如果约束被延迟,那么到事务结束检查约束时如果仍然因为存在一个引用行而违反外键约束,则仍会产生错...
autovacuum_analyze_scale_factor:默认10%。当update,insert,delete的tuples数量超过autovacuum_analyze_scale_factor*table_size+autovacuum_analyze_threshold时,进行analyze。 autovacuum_freeze_max_age:200 million。离下一次进行xid冻结的最大事务数。 autovacuum_multixact_freeze_max_age:400 million。离下一次进行xid...
# SET DEFAULT 主表在 on delete/update 时,设置从表外键为 DEFAULT(默认值)。 CREATE TABLE products ( product_no integer PRIMARY KEY, name text, price numeric ); CREATE TABLE orders ( order_id integer PRIMARY KEY, shipping_address text, ... ); CREATE TABLE order_items ( product_no integer...
DELETEFROMtable_name 删除指定行 代码语言:javascript 代码运行次数:0 运行 AI代码解释 DELETEFROMtable_nameWHEREprice=10; 增加列(使用ALTER语句) 代码语言:javascript 代码运行次数:0 运行 AI代码解释 ALTERTABLEtable_nameADDCOLUMNdescription text; 移除列(使用ALTER DROP语句) ...