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What is a trigger in Postgres?
A “trigger” is defined as any event that sets a course of action in a motion. In PostgreSQL, if you want to take action on specific database events, such as INSERT, UPDATE, DELETE, or TRUNCATE, then trigger functionality can be useful as it will invoke the required function on defined events.
How does trigger work in PostgreSQL?
PostgreSQL Triggers are database callback functions, which are automatically performed/invoked when a specified database event occurs. A trigger that is marked FOR EACH ROW is called once for every row that the operation modifies.
How do I get triggers in PostgreSQL?
To see the trigger you can make \dS , it shows not only columns of this table, but also all triggers defined on this table. To show the source of the trigger-function (or any function) use \df+ . Use \ef for more convenient reads.
What is Tg_op in PostgreSQL?
PL/pgSQL can be used to define trigger procedures. A trigger procedure is created with the CREATE FUNCTION command, declaring it as a function with no arguments and a return type of trigger. When a PL/pgSQL function is called as a trigger, several special variables are created automatically in the top-level block.
Does PostgreSQL have database-level triggers?
PostgreSQL Triggers are database callback functions, which are automatically performed/invoked when a specified database event occurs. The following are important points about PostgreSQL triggers − Before the operation is attempted on a row (before constraints are checked and the INSERT, UPDATE or DELETE is attempted)
What is an example of a trigger in SQL?
A SQL trigger is a database object just like a stored procedure, or we can say it is a special kind of stored procedure which fires when an event occurs in a database. We can execute a SQL query that will “do something” in a database when an event is fired. For example, a trigger can be set on a record insert in a database table.
What is an example of a database trigger?
The trigger is mostly used for maintaining the integrity of the information on the database. For example, when a new record (representing a new worker) is added to the employees table, new records should also be created in the tables of the taxes, vacations and salaries.