There are three times when a trigger can fire:
??? Before the execution of the triggering event
??? After the execution of the triggering event
??? Instead of the triggering event
Combining the first two timing options with the row and statement versions of a
trigger gives youfou r possible trigger implementations: before a statement, before a
row, after a statement, and after a row.
108 | Chapter 4: Oracle Data Structures
Oracle Database 11g introduced the concept of compound triggers; with this
enhancement, a single trigger can have a section for the different timing implementations.
Compound triggers help to improve performance, since the trigger has to be
loaded only once for multiple timing options.
INSTEAD OF triggers were introduced with Oracle8. The INSTEAD OF trigger has
a specific purpose: to implement data-manipulation operations on views that don??™t
normally permit them, such as a view that references columns in more than one base
table for updates. You should be careful when using INSTEAD OF triggers because
of the many potential problems associated with modifying the data in the underlying
base tables of a view.
Pages:
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253