In general, you can write to the columns of only one underlying base table of a view
in a single SQL statement. There are additional restrictions for INSERT, UPDATE,
and DELETE operations, and there are certain SQL clauses that prevent you from
updating any of the data in a view.
You can write to a nonupdateable view by using an INSTEAD OF trigger, which is
described later in this chapter.
Oracle8i introduced materialized views. These are not really views as defined in this
section, but are physical tables that hold presummarized data providing significant
performance improvements in a data warehouse. Materialized views are described in
more detail in Chapter 10.
Indexes
An index is a data structure that speeds up access to particular rows in a database.
An index is associated with a particular table and contains the data from one or more
columns in the table.
92 | Chapter 4: Oracle Data Structures
The basic SQL syntax for creating an index is shown in this example:
CREATE INDEX emp_idx1 ON emp (ename, job);
in which emp_idx1 is the name of the index, emp is the table on which the index is created,
and ename and job are the column values that make up the index.
Pages:
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217