You can specify table.fieldname in column setting which will be used in  where clause:

$col[“dbname”] = “table1.A”;

This was not solved my problem, because I need to search on combined table…

The easiest solution would be to shift your UNION query in a subquery and use parent query in grid. This way UNION’d tables will be treated as single table of subquery.

e.g.

SELECT column1, column2, column3 FROM
(
Select A as column1 , B as column2 , C as column3 FROM Table1
UNION
Select D as column1 , E as column2 , F as column3 FROM Table2
UNION
Select G as column1 , H as column2 , I as column3 FROM Table3
) as t

i had to do this in jqgrid_dist.php to add filters to unions in query

this on sql_count

$sql_count = $this->select_command.$wh;
                if (!empty($wh))
                {
                  $union= strrpos($sql_count,’union’);
                  if ($union !== false)
                     {
                        $sql_count= str_replace(‘union’, $wh.’ union ‘, $sql_count);
                     }
                  }

                $sql_count = “SELECT count(*) as c FROM (“.$sql_count.”) pg_tmp”;

and this on sql_query

 $sel_comm=$this->select_command.$wh;
                if (!empty($wh))
                {
                  $union= strrpos($sel_comm,’union’);
                  if ($union !== false)
                     {
                        $sel_comm= str_replace(‘union’, $wh.’ union ‘, $sel_comm);
                     }
                    // phpgrid_error($sql_count);
                  }

// coment this line
// $this->select_command.$wh.” ORDER BY $sidx $sord LIMIT $limit OFFSET $start”;

// and use this
$SQL = $sel_comm.” ORDER BY $sidx $sord LIMIT $limit OFFSET $start”;