Jabber Search for advanced user search - xmpp

Question

I'm trying to search user by username in my xmpp server, but the result always contains no items...
for getting the form format I send:
<iq type='get' to='search.MY_SERVER' xmlns='jabber:client'>
<query xmlns='jabber:iq:search'/>
</iq>
and received:
<iq xmlns="jabber:client" type="result" id="3:sendIQ" from="search.MY_SERVER" to="ID#MY_SERVER/7acf23bb">
<query xmlns="jabber:iq:search">
<instructions>The following fields are available for searching. Wildcard (*) characters are allowed as part of the query.</instructions>
<first/><last/><nick/><email/>
<x xmlns="jabber:x:data" type="form">
<title>Advanced User Search</title>
<instructions>The following fields are available for searching. Wildcard (*) characters are allowed as part of the query.</instructions>
<field var="FORM_TYPE" type="hidden">
<value>jabber:iq:search</value>
</field>
<field var="search" type="text-single" label="Search">
<required/>
</field>
<field var="Username" type="boolean" label="Username">
<value>1</value>
</field>
<field var="Name" type="boolean" label="Name">
<value>1</value>
</field>
<field var="Email" type="boolean" label="Email">
<value>1</value>
</field>
</x>
</query>
</iq>
and then I send:
<iq type='set' to='search.MY_SERVER' xmlns='jabber:client'>
<query xmlns='jabber:iq:search'>
<x xmlns='jabber:x:data' type='submit'>
<field type='hidden' var='FORM_TYPE'>
<value>jabber:iq:search</value>
</field>
<field var='search'>
<value>*</value>
</field>
</x>
</query>
</iq>
but received no items:
<iq xmlns="jabber:client" type="result" id="4:sendIQ" from="search.MY_SERVER" to="ID#MY_SERVER/7acf23bb">
<query xmlns="jabber:iq:search">
<x xmlns="jabber:x:data" type="result">
<field var="FORM_TYPE" type="hidden"/>
<reported>
<field var="jid" type="jid-single" label="JID"/>
<field var="Username" type="text-single" label="Username"/>
<field var="Name" type="text-single" label="Name"/>
<field var="Email" type="text-single" label="Email"/>
</reported>
</x>
</query>
</iq>
Does someone know what went wrong?

Answer 1

I have found the answer,send following request will do the trick:
<iq type='set' to='search.MY_SERVER' xmlns='jabber:client'>
<query xmlns='jabber:iq:search'>
<x xmlns='jabber:x:data' type='submit'>
<field var='search'>
<value>SEARCH_CRITERIA</value>
</field>
<field var='Username'>
<value>1</value>
</field>
</x>
</query>
</iq>