上题: In this tutorial you will create a stored procedure and triggers to check a complex constraint. Consider the table definition below: While the unique constraints defined here are sensible, they are not sufficient to express the constraint that a…
BCNF是比第三范式更严格一个范式.它要求关系模型中所有的属性(包括主属性和非主属性)都不传递依赖于任何候选关键字.也就是说,当关系型表中功能上互相依赖的那些列的每一列都是一个候选关键字时候,该满足BCNF. BCNF实际上是在第三范式的基础上,进一步消除了主属性的传递依赖. 一次Lab的作业题目如下: A luxury car-rental company has been tracking their rental data in a simple spreadsheet, but now…
一.创建事件触发器 1.ddl_command_start - 一个DDL开始执行前被触发: 2.ddl_command_end - 一个DLL 执行完成后被触发: 3.sql_drop -- 删除一个数据库对象前被触发: create or replace function abort_any_command() returns event_trigger language plpgsql as $$ begin raise exception 'command % is disabled',…
1 前言 功能需求:当一张表格某个字段变化,另一张表某个字段写入该值 2 代码 CREATE OR REPLACE FUNCTION "public"."synStatus"() RETURNS "pg_catalog"."trigger" AS $BODY$ declare vl_status int; BEGIN SELECT status INTO vl_status FROM ordergoods WHERE orde…
Task 1: Open countries.xml, compose the following XQueries: 1. Return the area of Mongolia. 2. Return the names of all cities that have the same name as the country in which they are located. 3. Return the average population of Russian-speaking count…
