With triggers, it is trivial to automate the management of the creation and last modified date timestamp fields.Ī Trigger in PostgreSQL is a special type of user defined function that is automatically invoked by the PostgreSQL database any time a particular set of events occur at the row level (or statement level) within a table. This is done through the PostgreSQL feature known as triggers. Luckily, for those working with the PostgreSQL database there is a very easy to way to overcome this issue by remove the responsibility for setting and maintaining of these timestamps from developers and putting it into the hands of the database itself. The moment that the values within a modified timestamp can’t be trusted to be accurate, you’ve not only destroyed the utility that timestamp is meant to provide, but also turned a potential asset into a liability as any other code that relies on these timestamps breaks. No matter the length and breadth of your engineering standards, there is always that one developer who will not properly keep these values up to date and in doing so introduce very serious issues to a code base. While the creation timestamp is usually very straightforward to implement and enforce usage, making sure all developers on a team are always properly updating the date of last modification on every row across every table can become a tediously annoying management task. Knowing when a row was inserted and when it was last updated are important pieces of information that are used across all kinds of apps.Ī data synchronization tool might use a modified date to identify rows that have changed since the last sync, while a dating app might use the creation timestamp to identify spam accounts. “DateModified”, “updated_at”, “last_modified_date”,etc.). “DateCreated”,”date_created”,”created_at”.etc) and the date that the row was last modified (ie. In this tutorial, you have learned how to use the PostgreSQL DROP TRIGGER statement to delete a trigger from a table.Aside from a field named “id”, the next two most commonly found columns in a typical database table are usually some form of timestamp column to track the date the row was created at (ie. ON staff Code language: SQL (Structured Query Language) ( sql ) Third, use the DROP TRIGGER statement to delete the username_check trigger: DROP TRIGGER username_check This trigger will fire whenever you insert or update a row in the staff table (from the sample database): CREATE TRIGGER username_checkįOR EACH ROW EXECUTE PROCEDURE check_staff_user() Second, create a new trigger on the staff table to check the username of a staff. RAISE EXCEPTION 'Username cannot be NULL' Ĭode language: SQL (Structured Query Language) ( sql ) CREATE FUNCTION check_staff_user()īEGIN IF length(NEW.username) < 8 OR NEW.username IS NULL THEN RAISE EXCEPTION 'The username cannot be less than 8 characters' The username of staff must not be null and its length must be at least 8. Note that in SQL standard, trigger names are not local to tables so the statement is simply: DROP TRIGGER trigger_name Code language: SQL (Structured Query Language) ( sql ) PostgreSQL DROP TRIGGER exampleįirst, create a function that validates the username of a staff. By default, the DROP TRIGGER statement uses RESTRICT. Note that CASCADE option will also delete objects that depend on objects that depend on the trigger.įifth, use the RESTRICT option to refuse to drop the trigger if any objects depend on it. If the table belongs to a specific schema, you can use the schema-qualified name of the table e.g., schema_name.table_name.įourth, use the CASCADE option if you want to drop objects that depend on the trigger automatically. Third, specify the name of the table to which the trigger belongs. If you use IF EXISTS to delete a non-existing trigger, PostgreSQL issues a notice instead. Attempt to delete a non-existing trigger without specifying the IF EXISTS statement results in an error. Second, use IF EXISTS to conditionally delete the trigger only if it exists. ON table_name Code language: SQL (Structured Query Language) ( sql )įirst, specify the name of the trigger which you want to delete after the DROP TRIGGER keywords. To delete a trigger from a table, you use the DROP TRIGGER statement with the following syntax: DROP TRIGGER trigger_name Introduction to PostgreSQL DROP TRIGGER statement Summary: in this tutorial, you will learn how to use the PostgreSQL DROP TRIGGER to drop a trigger from a table.
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