CREATE TABLE orders ( order_id integer PRIMARY KEY, product_no integer REFERENCES products, quantity integer ); # 定义多个 Column 组成的外键,要求被约束列(外键)的数量和类型应该匹配被引用列(主键)的数量和类型。 CREATE TABLE t1 ( a integer PRIMARY KEY, b integer, c integer, FOREIGN KEY (b, ...
1. However, to drop a table that is referenced by a view or a foreign-key constraint of another table, CASCADE must be specified. 1. (CASCADE will remove a dependent view entirely, but in the foreign-key case it will only remove the foreign-key constraint, not the other table entirely....
The PostgreSQL FOREIGN KEY is a combination of columns with values based on the primary key values from another table. A foreign key constraint, also known as Referential integrity Constraint, specifies that the values of the foreign key correspond to actual values of the primary key in the othe...
constraint_type有四种:UNIQUE、PRIMARY KEY、CHECK、FOREIGN KEY 通过修改上边sql语句的table_name和constraint_type来进行相应的查询 警告
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 ...
In this post, I am sharing one option to Disable / Enable the Foreign Key Constraint in PostgreSQL. During data migration and testing purpose, Database Developer requires to disable Foreign key constraint of a Table. Once you disable constraint, then later you might need t...
ERROR: cannot truncate a table referenced in a foreign key constraint by a local table 截断本地协调器(coordinator)节点表数据对于分布式表是安全的,因为它们的行(如果有)将在分发过程中复制到 worker 节点。 undistribute_table undistribute_table() 函数撤消 create_distributed_table 或 create_reference_ta...
[,...])postgres=#altertablespacetest_tbsrenametoprod_tbs;postgres=#altertablespacetest_tbsownertotest;--删除表空间postgres=#\helpdroptablespaceCommand:DROPTABLESPACEDescription:removeatablespaceSyntax:DROPTABLESPACE[IFEXISTS]namepostgres=#droptablespaceprod_tbs;DROPTABLESPACE--删除完后,自动生成的目录也会被...
Foreign key –show you how to define foreign key constraints when creating a new table or adding foreign key constraints for existing tables. DELETE CASCADE –show you how to automatically delete rows in child tables when the corresponding rows in the parent table are deleted. CHECK constraint –...
禁用t2表外键约束检查 FOREIGN_KEY_CHECKS=0 然后drop t1 原表 再rename _t1_new t1 这种方式速度更快,也不会阻塞请求。但有风险,第一,drop表的瞬间到rename过程,原表t1是不存在的,遇到请求会报错;第二,如果因为bug或某种原因,旧表已删,新表rename失败,那就太晚了,但这种情况很少见。