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, ...
# 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, c) REFERENCES other_table (c1, c2) ); # many2many,添加一个中间表 order_items 来引用两个主表 products 和 ...
ALTER TABLE products ADD CHECK (name <> ''); ALTER TABLE products ADD CONSTRAINT some_name UNIQUE (product_no); ALTER TABLE products ADD FOREIGN KEY (product_group_id) REFERENCES product_groups; 要增加一个不能写成表约束的非空约束,使用下面语法: ALTER TABLE products ALTER COLUMN product_no SE...
要重建所有表的逻辑外键,您需要使用以下SQL命令:```bashsql`ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGN KEY(column1, column2,...)REFERENCES referenced_table(column1, column2,...);```其中,`table_name`是表名,`constraint_name`是外键约束名,`column1, column2,...`是外键涉及的...
Summary: in this tutorial, you will learn about the PostgreSQL foreign key and how to add foreign keys to tables using foreign key constraints. Introduction to PostgreSQL Foreign Key Constraint In PostgreSQL, a foreign key is a column or a group of columns in a table that uniquely identifies ...
ALTERTABLEproductsADDCOLUMNdescription textCHECK(description<>''); 二、删除列 要删除列,请使用如下命令: ALTERTABLEproductsDROPCOLUMNdescription; 列中的任何数据都会消失。涉及列的表约束也被删除。但是,如果该列被另一个表的外键约束引用,PostgreSQL 不会默默地删除该约束。您可以通过添加 CASCADE 来授权删除依赖于...
PostgreSQL Alter Table Exercises: Write a SQL statement to add a foreign key constraint named fk_job_id on job_id column of job_history table referencing to the primary key job_id of jobs table.
ALTER TABLE <target_table> ADD CONSTRAINT <foreign key constraint> FOREIGN KEY (<foreign_key_field>)REFERENCES <parent_table>(<primary key field>)...同样增加maintenance_work_mem配置参数也能提高重新创建外键约束的性能。暂停触发器 INSERT或DELETE触发器（如果导入过程还涉及从目标表中删除记录）可能会导致...
ALTER TABLE rental ADD CONSTRAINT fk_customer_id FOREIGN KEY (customer_id) REFERENCES customers(customer_id); 6. 排他约束: 排他约束确保表中没有两行满足指定的谓词,这使得你可以定义除简单唯一约束或检查约束之外的自定义约束。例如,你可能有一个“bookings”表,你希望确保同一个房间的两个预订在时间上不...
ALTER TABLE(包括RENAME TABLE、ADD COLUMN、ADD COLUMN DEFAULT、ALTER COLUMN TYPE、DROP COLUMN、ADD CONSTRAINT、ADD CONSTRAINT CHECK、ALTER COLUMN DROP DEFAULT) CREATE INDEX ON TABLE、DROP INDEX DROP RULE CREATE SEQUENCE、ALTER SEQUENCE RENAME TO、DROP SEQUENCE通过增...