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 ...
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, ...
maintenance_work_mem = 40MB # 指定在维护性操作(例如VACUUM、CREATE INDEX和ALTER TABLE ADD FOREIGN KEY)中使用的 最大的内存量。其默认值是 64 兆字节(64MB)。 # 因为在一个数据库会话中,一个时刻只有一个这样的操作可以被执行,并且一个数据库安装通常不会有太多这样的操作并发执行, # 把这个数值设置得...
1、增加maintenance_work_mem参数大小 增加这个参数可以提升CREATE INDEX和ALTER TABLE ADD FOREIGN KEY的执行效率。 2、增加checkpoint_segments参数的大小 增加这个参数可以提升大量数据导入时候的速度。 3、设置archive_mode无效 这个参数设置为无效的时候,能够提升以下的操作的速度 ・CREATE TABLE AS SELECT ・CREATE...
增加这个参数可以提升CREATE INDEX和ALTER TABLE ADD FOREIGN KEY的执行效率。 增加checkpoint_segments参数的大小 增加这个参数可以提升大量数据导入时候的速度。 设置archive_mode无效 这个参数设置为无效的时候,能够提升以下的操作的速度 CREATE TABLE AS SELECT ...
Previous:Write a SQL statement to add a foreign key on job_id column of job_history table referencing to the primary key job_id of jobs table. Next:Write a SQL statement to drop the existing foreign key fk_job_id from job_history table on job_id column, which is referenced to the jo...
JOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_name WHERE constraint_type = 'FOREIGN KEY'; 2. 根据外键名称,查找其对应的主键表名。在查询结果中,外键表名可以通过tc.table_name获取,主键表名可以通过ccu.table_name获取。发布...
If you want to see whether the table is actually created, issue the following command. \dt This will show you the table you have created, as shown in the following image. To delete an existing table issue the following command. DROP TABLE emp_data; ...
Alter table –modify the structure of an existing table. Rename table –change the name of the table to a new one. Add column – show you how to add one or more columns to an existing table. Drop column –demonstrate how to drop a column of a table. Change column data type –show...
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...