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<title>Tutorial: Creating a Trigger that Logs Table Changes</title>
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<p><a id="BABGEAIA" name="BABGEAIA"></a><a id="TDDDG52100" name="TDDDG52100"></a></p>
<div class="sect2">
<h1>Tutorial: Creating a Trigger that Logs Table Changes</h1>
<a name="BEGIN" id="BEGIN"></a>
<p>This tutorial shows how to use the <code>CREATE</code> <code>TRIGGER</code> statement to create a trigger, <code>EVAL_CHANGE_TRIGGER</code>, which adds a row to the table <code>EVALUATIONS_LOG</code> whenever an <code>INSERT</code>, <code>UPDATE</code>, or <code>DELETE</code> statement changes the <code>EVALUATIONS</code> table.</p>
<p>The trigger adds the row <span class="italic">after</span> the triggering statement executes, and uses the <a id="sthref566" name="sthref566"></a><span class="bold">conditional predicates</span> <a id="sthref567" name="sthref567"></a><code>INSERTING</code>, <a id="sthref568" name="sthref568"></a><code>UPDATING</code>, and <a id="sthref569" name="sthref569"></a><code>DELETING</code> to determine which of the three possible DML statements fired the trigger.</p>
<p><code>EVAL_CHANGE_TRIGGER</code> is a <a id="sthref570" name="sthref570"></a><a id="sthref571" name="sthref571"></a><span class="bold">statement-level trigger</span> and an <a id="sthref572" name="sthref572"></a><a id="sthref573" name="sthref573"></a><span class="bold">AFTER trigger</span>.</p>
<p>This trigger is part of the <a id="sthref574" name="sthref574"></a>sample application that the tutorials and examples in this document show how to develop and deploy.</p>
<a id="TDDDG249" name="TDDDG249"></a>
<p class="subhead2">To create EVALUATIONS_LOG and EVAL_CHANGE_TRIGGER:</p>
<ol>
<li>
<p>Create the <code>EVALUATIONS_LOG</code> table:</p>
<pre xml:space="preserve" class="oac_no_warn">
CREATE TABLE EVALUATIONS_LOG ( log_date DATE
                             , action VARCHAR2(50));
</pre></li>
<li>
<p>Create <code>EVAL_CHANGE_TRIGGER</code>:</p>
<pre xml:space="preserve" class="oac_no_warn">
CREATE OR REPLACE TRIGGER EVAL_CHANGE_TRIGGER
  <span class="bold">AFTER</span> INSERT OR UPDATE OR DELETE
  ON EVALUATIONS
DECLARE
  log_action  EVALUATIONS_LOG.action%TYPE;
BEGIN
  IF <span class="bold">INSERTING</span> THEN
    log_action := 'Insert';
  ELSIF <span class="bold">UPDATING</span> THEN
    log_action := 'Update';
  ELSIF <span class="bold">DELETING</span> THEN
    log_action := 'Delete';
  ELSE
    DBMS_OUTPUT.PUT_LINE('This code is not reachable.');
  END IF;

INSERT INTO EVALUATIONS_LOG (log_date, action)
    VALUES (SYSDATE, log_action);
END;
</pre></li>
</ol>
<div class="helpinfonotealso">
<h2>Related Topics</h2>
<p><a href="tdddg_triggers002.htm#BABDAGJJ">Creating Triggers</a></p>
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