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<refentry xml:id="function.mysqlnd-ms-query-is-select" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>mysqlnd_ms_query_is_select</refname>
  <refpurpose>Find whether to send the query to the master, the slave or the last used MySQL server</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>int</type>
   <methodname>mysqlnd_ms_query_is_select</methodname>
   <methodparam><type>string</type><parameter>query</parameter></methodparam>
  </methodsynopsis>
  <para>
   Finds whether to send the query to the master, the slave or the
   last used MySQL server.
  </para>
  <para>
   The plugins built-in read/write split mechanism
   will be used to analyze the query string to make a recommendation where
   to send the query. The built-in read/write split mechanism is very
   basic and simple. The plugin will recommend sending all queries to the
   MySQL replication master server but those which begin with
   <literal>SELECT</literal>, or begin with a SQL hint which
   enforces sending the query to a slave server. Due to the basic
   but fast algorithm the plugin may propose to run some read-only
   statements such as <literal>SHOW TABLES</literal> on the replication master.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <variablelist>
   <varlistentry>
    <term><parameter>query</parameter></term>
    <listitem>
     <para>
     Query string to test.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   A return value of <constant>MYSQLND_MS_QUERY_USE_MASTER</constant>
   indicates that the query should be send to the MySQL replication
   master server. The function returns a value of
   <constant>MYSQLND_MS_QUERY_USE_SLAVE</constant> if the query can be run
   on a slave because it is considered read-only. A value of
   <constant>MYSQLND_MS_QUERY_USE_LAST_USED</constant> is returned to recommend
   running the query on the last used server. This can either be a MySQL
   replication master server or a MySQL replication slave server.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>mysqlnd_ms_query_is_select</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
function is_select($query)
{
 switch (mysqlnd_ms_query_is_select($query))
 {
  case MYSQLND_MS_QUERY_USE_MASTER:
   printf("'%s' should be run on the master.\n", $query);
   break;
  case MYSQLND_MS_QUERY_USE_SLAVE:
   printf("'%s' should be run on a slave.\n", $query);
   break;
  case MYSQLND_MS_QUERY_USE_LAST_USED:
   printf("'%s' should be run on the server that has run the previous query\n", $query);
   break;
  default:
   printf("No suggestion where to run the '%s', fallback to master recommended\n", $query);
   break;
 }
}

is_select("INSERT INTO test(id) VALUES (1)");
is_select("SELECT 1 FROM DUAL");
is_select("/*" . MYSQLND_MS_LAST_USED_SWITCH . "*/SELECT 2 FROM DUAL");
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
INSERT INTO test(id) VALUES (1) should be run on the master.
SELECT 1 FROM DUAL should be run on a slave.
/*ms=last_used*/SELECT 2 FROM DUAL should be run on the server that has run the previous query
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member>
     <link linkend="mysqlnd-ms.constants">Predefined Constants</link>
    </member>
   </simplelist>
  </para>
 </refsect1>
 
</refentry>

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