Trigger updating column


01-Jun-2015 16:01

# \d users Table "public.users" Column | Type | Modifiers ------------------+-------------------+---------------------------------------------------- id | integer | not null default nextval('users_id_seq'::regclass) username | character varying | not null password | character varying | not null password_changed | date | default now() Indexes: "users_username_key" UNIQUE CONSTRAINT, btree (username) Triggers: trigger_password_changed BEFORE UPDATE ON users FOR EACH ROW EXECUTE PROCEDURE List of functions -[ RECORD 1 ]-------+----------------------------------------- Schema | public Name | password_changed Result data type | trigger Argument data types | Type | trigger Security | invoker Volatility | volatile Owner | postgres Language | plpgsql Source code | | BEGIN | IF NEW.password != OLD.password THEN | NEW.password_changed := current_date; | END IF; | RETURN NEW; | END; Because the trigger is defined within the database it will survive any normal backup and restore process unaffected.We can create a trigger to update the 'product_price_history' table when the price of the product is updated in the 'product' table.1) Create the 'product' table and 'product_price_history' table Once the above update query is executed, the trigger fires and updates the 'product_price_history' table.

trigger updating column-71

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We have a simple database of usernames and (encrypted) passwords with the following definition: Rather than tackling each of these independently, using a trigger we can address them all at the same time, and all from within the database.

We create our trigger function using PL/pg SQL - which comes built in in Postgre SQL 9.0 and later, and can be installed as an add-on for earlier versions.

4)If you ROLLBACK the transaction before committing to the database, the data inserted to the table is also rolled back.

There are two types of triggers based on the which level it is triggered.

A trigger is a pl/sql block structure which is fired when a DML statements like Insert, Delete, Update is executed on a database table.A trigger is triggered automatically when an associated DML statement is executed.



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