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<title>About Exceptions and Exception Handlers</title>
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<p><a id="BABFIBHE" name="BABFIBHE"></a><a id="TDDDG99947" name="TDDDG99947"></a></p>
<div class="sect2">
<h1>About Exceptions and Exception Handlers</h1>
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<p><a id="sthref524" name="sthref524"></a>When a run-time error occurs in PL/SQL code, an <span class="bold">exception</span> is raised. If the subprogram (or block) in which the exception is raised has an exception-handling part, control transfers to it; otherwise, execution stops.</p>
<p>Run-time errors can arise from design faults, coding mistakes, hardware failures, and many other sources. Because you cannot anticipate all possible errors, Oracle recommends including exception-handling parts in your subprograms (<a href="tdddg_subprograms006.htm#BABJGJGJ">"About Subprogram Structure"</a> shows where to put the exception-handling part).</p>
<p>Oracle Database has many <a id="sthref525" name="sthref525"></a><span class="bold">predefined exceptions</span>, which it raises automatically when a program violates database rules or exceeds system-dependent limits. For example, if a <code>SELECT</code> <code>INTO</code> statement returns no rows, Oracle Database raises the predefined exception <code>NO_DATA_FOUND</code>. For a summary of predefined PL/SQL exceptions, see <a href="javascript:open('http://www.oracle.com/pls/db112/lookup?id=LNPLS00703','newWindow').focus()"><span class="italic">Oracle Database PL/SQL Language Reference</span></a>.</p>
<p>PL/SQL lets you define (declare) your own exceptions. An exception declaration has this syntax:</p>
<pre xml:space="preserve" class="oac_no_warn">
<span class="italic">exception_name</span> EXCEPTION;
</pre>
<p>Unlike a predefined exception, a <a id="sthref526" name="sthref526"></a><span class="bold">user-defined exception</span> must be raised explicitly, using either the <a id="sthref527" name="sthref527"></a><code>RAISE</code> statement or the <a id="sthref528" name="sthref528"></a><a id="sthref529" name="sthref529"></a><code>DBMS_STANDARD</code>.<code>RAISE_APPLICATION_ERROR</code> procedure. For example:</p>
<pre xml:space="preserve" class="oac_no_warn">
IF <span class="italic">condition</span> THEN RAISE <span class="italic">exception_name</span>;
</pre>
<p>For information about the <code>DBMS_STANDARD</code>.<code>RAISE_APPLICATION_ERROR</code> procedure, see <a href="javascript:open('http://www.oracle.com/pls/db112/lookup?id=LNPLS99960','newWindow').focus()"><span class="italic">Oracle Database PL/SQL Language Reference</span></a>.</p>
<p>The exception-handling part of a subprogram contains one or more exception handlers. An <a id="sthref530" name="sthref530"></a><span class="bold">exception handler</span> has this syntax:</p>
<pre xml:space="preserve" class="oac_no_warn">
WHEN { <span class="italic">exception_name</span> [ OR <span class="italic">exception_name</span> ]... | OTHERS } THEN
  <span class="italic">statement</span>; [ <span class="italic">statement</span>; ]...
</pre>
<p>A <a id="sthref531" name="sthref531"></a><code>WHEN</code> <code>OTHERS</code> exception handler handles unexpected run-time errors. If used, it must be last. For example:</p>
<pre xml:space="preserve" class="oac_no_warn">
EXCEPTION
  WHEN <span class="italic">exception_1</span> THEN
    <span class="italic">statement</span>; [ <span class="italic">statement</span>; ]...
  WHEN <span class="italic">exception_2</span> OR <span class="italic">exception_3</span> THEN
    <span class="italic">statement</span>; [ <span class="italic">statement</span>; ]...
  WHEN OTHERS THEN
    <span class="italic">statement</span>; [ <span class="italic">statement</span>; ]...
END;
</pre>
<p>An alternative to the <code>WHEN</code> <code>OTHERS</code> exception handler is the <a id="sthref532" name="sthref532"></a><code>EXCEPTION_INIT</code> pragma, which associates a user-defined exception name with an Oracle Database error number.</p>
<div class="helpinfonotealso">
<h2>Related Topics</h2>
<p><a href="javascript:open('http://www.oracle.com/pls/db112/lookup?id=LNPLS01387','newWindow').focus()"><span class="italic">Oracle Database PL/SQL Language Reference</span></a> for more information about exception declaration syntax</p>
<p><a href="javascript:open('http://www.oracle.com/pls/db112/lookup?id=LNPLS01316','newWindow').focus()"><span class="italic">Oracle Database PL/SQL Language Reference</span></a> for more information about exception handler syntax</p>
<p><a href="javascript:open('http://www.oracle.com/pls/db112/lookup?id=LNPLS01315','newWindow').focus()"><span class="italic">Oracle Database PL/SQL Language Reference</span></a> for more information about the <code>EXCEPTION_INIT</code> pragma</p>
<p><a href="tdddg_subprograms049.htm#CIHIHAFG">Handling Exceptions (Run-Time Errors)</a></p>
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