Searching is supported out of the box in all methods listed below . The component supports both single search and multiple searching.
The exception here is that when the grid is used in configuration with queryGrid, editGrid and exportToExcel as separate methods the filterToolbar method in jqGrid Javascript lib should be configured to post the search values as string. You can see details of that below.

Related methods
exportToExcel
queryGrid
editGrid
renderGrid

Below is an example how to configure filterToolbar to be synchronized with the queryGrid, editGrid and exportToExcel methods.
Using again our example the code can look like this:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>PHP jqGrid Class Example</title> 

<link rel="stylesheet" type="text/css" media="screen" href="themes/redmond/jquery-ui-1.7.1.custom.css" />
<link rel="stylesheet" type="text/css" media="screen" href="themes/ui.jqgrid.css" />

<script src="js/jquery-1.3.2.min.js" type="text/javascript"></script>
<script src="js/i18n/grid.locale-en.js" type="text/javascript"></script>
<script src="js/jquery.jqGrid.min.js" type="text/javascript"></script>
<script type="text/javascript">
jQuery(document).ready(function(){
....
// Craeate the grid manually
jQuery("#grid").jqGrid({
"colModel":[
     {"name":"OrderID","index":"OrderID","label":"ID","width":60, "key":true},
     {"name":"OrderDate","index":"OrderDate"},
     {"name":"CustomerID","index":"CustomerID"},
     {"name":"Freight","index":"Freight"},
     {"name":"ShipName","index":"ShipName"}
],
"url":"querygrid.php",
"datatype":"json",
"jsonReader":{repeatitems:false},
"pager":"#pager"
});
// Set filterToolbar to post the search parameters as string
jQuery("#grid").jqGrid('filterToolbar',{stringResult: true});
......
});
</script>

</head>
<body>
......
<table id="grid"></table>
<div id="pager"></div>
.......
</body>
</html>

There is no need to change any PHP code.