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What are triggers and views?
By using INSTEAD OF triggers, we can change the behavior of INSERT, UPDATE and DELETE statements for a given view. In other words, we can perform certain validations before making a change to the data. With the combination of a view and a trigger you can create row and cell level security on tables.
Do MySQL support triggers and views?
Important: MySQL triggers activate only for changes made to tables by SQL statements. They do not activate for changes in views, nor by changes to tables made by APIs that do not transmit SQL statements to the MySQL server.
What are views and triggers in SQL?
A trigger is a special type of stored procedure that automatically runs when an event occurs in the database server. DML triggers run when a user tries to modify data through a data manipulation language (DML) event. DML events are INSERT, UPDATE, or DELETE statements on a table or view.
What is a triggers in MySQL?
A MySQL trigger is a stored program (with queries) which is executed automatically to respond to a specific event such as insertion, updation or deletion occurring in a table.
Can we use triggers in views?
You can use the trigger action to update the tables underlying the view, in some cases updating an otherwise “non-updatable” view. You can also use INSTEAD OF triggers to substitute other actions when INSERT, DELETE, or UPDATE statements reference specific columns within the database.
Can a MySQL trigger be activated on a view?
Contrary to what the documentation states, we can activate triggers even while operating on views: https://dev.mysql.com/doc/refman/5.7/en/triggers.html Important: MySQL triggers activate only for changes made to tables by SQL statements.
How are MySQL triggers used to affect queries?
In this post we’ll review how MySQL triggers can affect queries. Contrary to what the documentation states, we can activate triggers even while operating on views: Important: MySQL triggers activate only for changes made to tables by SQL statements.
What’s the difference between a trigger and a rule?
Triggers And Rules. Triggers are objects generally tied to a table or view that run code based on certain events such as inserting data, before inserting data, updating/deleting data and before these events happen. Triggers can be very great things and very dangerous things.
How many views can be defined in SQL?
3 (A view can often be defined with an administrative designer or using a color coded sql editor so is fairly easy to read) – in general though it is limited to only one select statement or unioned select statements.