jQuery Grid Plugin - jqGrid

Hi ! I am very new in jqGrid. I am trying jqGrid and I have the following problem: After creating jqGrid I want to edit  a row from the grid (row from sql table).  How can be validated entry name (for example) with sql query  using :

$onsubmit = <<<ONSUBMIT

function(rowid,selected)

{

(hire i have to execute some sql query)

If (result of query  is ok )

{

$grid->update();

return(true,'Update is ok');

else {

Return(false,'Cannot update');

}

}

ONSUBMIT;

$grid->setGridEvent('beforesubmit',$onsubmit);