For example, the following trigger cancels person node deletion if there are any open auctions referenced by this person: To understand how trigger behavior works, you need to be aware of the two main types of triggers; these are Row and Statement level triggers.The distinction between the two is how many times the code within the trigger is executed, and at what time.These trigger types are referred to as "Schema-level triggers". Performing conditional actions in triggers (or testing data following modification) is done through accessing the temporary Inserted and Deleted tables. The following functionality in SQL:2003 was previously not implemented in Postgre SQL: Firebird supports multiple row-level, BEFORE or AFTER, INSERT, UPDATE, DELETE (or any combination thereof) triggers per table, where they are always "in addition to" the default table changes, and the order of the triggers relative to each other can be specified where it would otherwise be ambiguous (POSITION clause.) Triggers may also exist on views, where they are always "instead of" triggers, replacing the default updatable view logic.
A database trigger is procedural code that is automatically executed in response to certain events on a particular table or view in a database.The trigger is mostly used for maintaining the integrity of the information on the database.An example of implementation of triggers in non-relational database can be Sedna, that provides support for triggers based on XQuery.Triggers in Sedna were designed to be analogous to SQL:2003 triggers, but natively base on XML query and update languages (XPath, XQuery and XML update language).The code within the trigger is executed after the INSERT happens to the table.
An example use of this trigger is creating an audit history of who has made inserts into the database, keeping track of the changes made.A trigger in Sedna is set on any nodes of an XML document stored in database.When these nodes are updated, the trigger automatically executes XQuery queries and updates specified in its body.Suppose you have a trigger that is made to be called on an UPDATE to a certain table.Row level triggers would execute once for each row that is affected by the UPDATE.Below follows a series of descriptions of how some popular DBMS support triggers.