PostgreSQL: Documentation: 8.1: Writing Trigger Functions in C.
To create a new trigger in PostgreSQL, you follow these steps: First, create a trigger function using CREATE FUNCTION statement. Second, bind the trigger function to a table by using CREATE TRIGGER statement. If you are not familiar with creating a user-defined function, you can check it out the PostgreSQL stored procedure section.
DROP a PostgreSQL trigger To delete or destroy a trigger, use a DROP TRIGGER statement. To execute this command, the current user must be the owner of the table for which the trigger is defined.
The documentation of each procedural language explains how to write a trigger in that language. Trigger functions must use the “ version 1 ” function manager interface. When a function is called by the trigger manager, it is not passed any normal arguments, but it is passed a “ context ” pointer pointing to a TriggerData structure.
But it would be easy to write a BEFORE DELETE trigger that ensures the condition:. What about these “constraint triggers”? Finally, PostgreSQL has the option to create “constraint triggers” with CREATE CONSTRAINT TRIGGER. It sounds like such triggers could be used to avoid the race condition.
I am writing a trigger that needs to raise an exception if a condition doesn't hold. That condition that should result in a raise is that the current row being modified has a field enrolled that is null, and the primary key of the row being modified does not appear in one of 6 other tables. (I know that this is a terrible design, but this is what I've inherited, and I don't have much.
Coming from Microsoft SQL Server, I keep on forgetting how to return a resultset from a stored procedure in postgresql. Here is a small sample of how to do it. Needs a bit more code than SQL Server. Note that postgresql does not have stored procedure, they have function. They are equivalent.
I need to write validation trigger for a table. Due to nature of validation I can not use builtin integrity checks. For purpose of this question let's say that validation counts number of rows with specific properties and number of this rows has to be less than 5.
PostgreSQL functions, also known as Stored Procedures, allow you to carry out operations that would normally take several queries and round trips in a single function within the database.Functions allow database reuse as other applications can interact directly with your stored procedures instead of a middle-tier or duplicating code.
The documentation of each procedural language explains how to write a trigger in that language. Trigger functions must use the “version 1” function manager interface. When a function is called by the trigger manager, it is not passed any normal arguments, but it is passed a “context” pointer pointing to a TriggerData structure.
There's work in PostgreSQL 9.4 to make ALTER TABLE take weaker locks for some operations. It might help with this. In the mean time, I'd CREATE OR REPLACE FUNCTION to replace the trigger with a simple no-op function. Then, to actually drop the trigger, I'd probably write a script that does.
We have been writing blog posts about how to write simple extensions in C language and a little more complex one by Ibrar which were well received by PostgreSQL user community. Then we observed that many PostgreSQL users create simple triggers for small auditing requirements, and then feel the pain of trigger on transactions.
I'm now playing a DBA role too and writing both regular functions and trigger functions on my databases as needed. If I find the same logic appearing in more than one trigger function, is it considered an ok practice in PostgreSQL to factor that code block into its own function that's called under the appropriate conditions by the trigger functions that need it?
How to Query a JSON Column in PostgreSQL. One of PostgreSQL's benefits is that it's a relational database, but you can also get the advantages of unstructured data by storing things in a JSON column. Here's how you can query your JSON column in PostgreSQL.
