PostgreSQL Documentation 16 CREATE RULE
Description CREATE RULE defines a new rule applying to a specified table or view CREATE OR REPLACE RULE will either create a new rule or replace an existing rule of the same name for the same table The PostgreSQL rule system allows one to define an alternative action to be performed on insertions updates or deletions in database tables Roughly speaking a rule causes additional commands
What are PostgreSQL RULEs good for Stack Overflow, 21 One of the use cases for RULES are updateable views although that changes in 9 1 as that version introduces INSTEAD OF triggers for views Another good explanation can be found in the manual For the things that can be implemented by both which is best depends on the usage of the database A trigger is fired for any affected row once
41 4 Rules on INSERT UPDATE and DELETE PostgreSQL
In mind In the following update rules means rules that are defined on INSERT UPDATE or DELETE Update rules get applied by the rule system when the result relation and the command type of a query tree are equal to the object and event given in the CREATE RULE command For update rules the rule system creates a list of query trees
Rules in PostgreSQL SQLServerCentral, The PostgreSQL rule system allows to define an alternative action on insert update or delete A rule generates an extra query As a result rule execution impacts the performance of the system
PostgreSQL Documentation 16 41 2 Views and the Rule System
PostgreSQL Documentation 16 41 2 Views and the Rule System, Views in PostgreSQL are implemented using the rule system A view is basically an empty table having no actual storage with an ON SELECT DO INSTEAD rule Conventionally that rule is named RETURN So a view like CREATE VIEW myview AS SELECT FROM mytab is very nearly the same thing as CREATE TABLE myview same column list as mytab
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PostgreSQL Documentation 16 41 7 Rules Versus Triggers
PostgreSQL Documentation 16 41 7 Rules Versus Triggers 41 7 Rules Versus Triggers Many things that can be done using triggers can also be implemented using the PostgreSQL rule system One of the things that cannot be implemented by rules are some kinds of constraints especially foreign keys It is possible to place a qualified rule that rewrites a command to NOTHING if the value of a column
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PostgreSQL Rules are used to intercept and change a query before it s executed For example lets say you have a table people can add stuff to but you need to put 3 entries in the table which can never be changed or removed This is how you do it Lets create an example table foo CREATE TABLE gift certificates idnum serial person Introduction to PostgreSQL Rules Making entries which can t be . The Rule System 40 5 Rules and Privileges Due to rewriting of queries by the PostgreSQL rule system other tables views than those used in the original query get accessed When update rules are used this can include write access to tables Rewrite rules don t have a separate owner The owner of a relation table or view is automatically Many things that can be done using triggers can also be implemented using the PostgreSQL rule system One of the things that cannot be implemented by rules are some kinds of constraints especially foreign keys Here we show an example of how the choice of rules versus triggers plays out in one situation There are two tables CREATE TABLE
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