ch5 Programs to Access a Database.pptVIP

5.3 Trigger Triggers are commonly used to: prevent changes (e.g. prevent an invoice from being changed after its been mailed out) log changes (e.g. keep a copy of the old data) audit changes (e.g. keep a log of the users and roles involved in changes) 5.3 Trigger Triggers are commonly used to: enhance changes (e.g. ensure that every change to a record is time-stamped by the servers clock, not the clients) prevent changes (e.g. prevent an invoice from being changed after its been mailed out) 5.3 Trigger Triggers are commonly used to: log changes (e.g. keep a copy of the old data) audit changes (e.g. keep a log of the users and roles involved in changes) enhance changes (e.g. ensure that every change to a record is time-stamped by the servers clock, not the clients) 5.3 Trigger Triggers are commonly used to: enforce business rules (e.g. require that every invoice have at least one line item) execute business rules (e.g. notify a manager every time an employees bank account number changes) 5.3 Trigger Triggers are commonly used to: replicate data (e.g. store a record of every change, to be shipped to another database later) enhance performance (e.g. update the account balance after every detail transaction, for faster queries) 5.3 Trigger The major features of database triggers and their effects: do not accept parameters or arguments (but may store affected-data in temporary tables) can not perform commit or rollback operations because they are part of the triggering SQL statement (only through autonomous transactions) can cancel a requested operation can cause mutating table errors 5.3 Trigger Triggering events that cause triggers to execute: INSERT?event (as a new record is being inserted into the database). UPDATE?event (as a record is being changed). DELETE?event (as a record is being deleted). 5.3 Trigger AFTER|FOR -type triggers : run after any changes already being made to the database. INSTEAD OF -type triggers : fully replace the databases normal ac