What are the updating rules for pgsql?
In PostgreSQL, an update rule is used to define how data is updated in a table when updating data. Update rules can be implemented using triggers or rules.
A trigger is a function that is automatically executed when a specific event occurs. In PostgreSQL, triggers can be defined on a table to automatically trigger corresponding actions when data is updated, inserted, or deleted. Triggers can be executed before, after, or instead of updating data.
Rules are a more advanced mechanism used to specify alternative actions in the query parsing and query rewriting process. They allow for queries to be automatically transformed into other queries during execution to achieve specific updating behavior.
The sequence for implementing the updates rules is as follows:
- Execute BEFORE triggers: Prior to the update operation being carried out, any BEFORE triggers associated with the table will be executed. These triggers have the ability to modify the data being updated or prevent the update operation from taking place.
- Perform update operation: Update data in the table based on the conditions and values specified in the update statement.
- Execute AFTER triggers: Following the update operation, any AFTER triggers associated with the table will be executed. These triggers can perform any additional necessary actions, such as logging or triggering other events.
It is important to note that during the execution of updated rules, triggers and rules can interact with and trigger each other. Therefore, when designing updated rules, it is necessary to ensure that there are no situations of infinite loops or deadlocks.
In summary, the updating rules of pgsql are implemented through triggers and rules, where triggers can perform operations before, after, or instead of an update, and rules allow for specifying alternative operations during query parsing and rewriting.
