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<p><a id="BABECIAE" name="BABECIAE"></a><a id="TDDDG52800" name="TDDDG52800"></a></p>
<div class="sect2">
<h1>Creating an INSTEAD OF Trigger</h1>
<a name="BEGIN" id="BEGIN"></a>
<p>A view presents the output of a query as a table. If you want to change a view as you would change a table, you must create <a id="sthref581" name="sthref581"></a><a id="sthref582" name="sthref582"></a><a id="sthref583" name="sthref583"></a><a id="sthref584" name="sthref584"></a><code>INSTEAD</code> <code>OF</code> triggers. Instead of changing the view, they change the underlying tables.</p>
<p>For example, consider the view <code>EMP_LOCATIONS</code>, whose <code>NAME</code> column is created from the <code>LAST_NAME</code> and <code>FIRST_NAME</code> columns of the <code>EMPLOYEES</code> table:</p>
<pre xml:space="preserve" class="oac_no_warn">
CREATE VIEW EMP_LOCATIONS AS
SELECT e.EMPLOYEE_ID,
  <span class="bold">e.LAST_NAME || ', ' || e.FIRST_NAME NAME</span>,
  d.DEPARTMENT_NAME DEPARTMENT,
  l.CITY CITY,
  c.COUNTRY_NAME COUNTRY
FROM <span class="bold">EMPLOYEES e</span>, DEPARTMENTS d, LOCATIONS l, COUNTRIES c
WHERE e.DEPARTMENT_ID = d.DEPARTMENT_ID AND
 d.LOCATION_ID = l.LOCATION_ID AND
 l.COUNTRY_ID = c.COUNTRY_ID
ORDER BY LAST_NAME;
</pre>
<p>To update <code>EMP_LOCATIONS</code>.<code>NAME</code>, you must update <code>EMPLOYEES</code>.<code>LAST_NAME</code> and <code>EMPLOYEES</code>.<code>FIRST_NAME</code>. This is what the <code>INSTEAD</code> <code>OF</code> trigger in the following example does.</p>
<p>This trigger is part of the <a id="sthref585" name="sthref585"></a>sample application that the tutorials and examples in this document show how to develop and deploy.</p>
<p><code>NEW</code> and <code>OLD</code> are <span class="bold">pseudorecords</span> that the PL/SQL run-time engine creates and populates whenever a row-level trigger fires. <code>OLD</code> and <code>NEW</code> store the original and new values, respectively, of the record being processed by the trigger. They are called pseudorecords because they do not have all properties of PL/SQL records.</p>
<div class="example"><a id="BABBFAGD" name="BABBFAGD"></a><a id="TDDDG251" name="TDDDG251"></a>
<p class="titleinexample">Creating an INSTEAD OF Trigger</p>
<pre xml:space="preserve" class="oac_no_warn">
CREATE OR REPLACE TRIGGER update_name_view_trigger
<span class="bold">INSTEAD OF UPDATE ON emp_locations</span>
BEGIN
  <span class="bold">UPDATE employees SET</span>
    <span class="bold">first_name = substr( :NEW.name, instr( :new.name, ',' )+2),</span>
    <span class="bold">last_name = substr( :NEW.name, 1, instr( :new.name, ',')-1)</span>
  <span class="bold">WHERE employee_id = :OLD.employee_id;</span>
END;
</pre></div>

<div class="helpinfonotealso">
<h2>Related Topics</h2>
<p><a href="javascript:open('http://www.oracle.com/pls/db112/lookup?id=LNPLS20041','newWindow').focus()"><span class="italic">Oracle Database PL/SQL Language Reference</span></a></p>
<p><a href="tdddg_triggers002.htm#BABDAGJJ">Creating Triggers</a></p>
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