R=Error: Couldn't execute query. No database selected – SELECT i.id, invdate , c.name, i.note, i.total, i.closed FROM invheader i INNER JOIN clients c ON c.client_id = i.client_id WHERE 1=1 LIMIT 1 OFFSET 0

/* INDEX.PHP */
<?php

// include db config
include_once("config.php");

// set up DB
mysqli_connect("localhost","user","password","database");

// include and create object
include(PHPGRID_LIBPATH."inc/jqgrid_dist.php");

// you can customize your own columns …

$col = array();
$col["title"] = "Id"; // caption of column
$col["name"] = "id"; // grid column name, must be exactly same as returned column-name from sql (tablefield or field-alias)
$col["width"] = "10";
# $col["hidden"] = true; // hide column by default
$cols[] = $col;

$col = array();
$col["title"] = "Client";
$col["name"] = "name";
$col["width"] = "100";
$col["editable"] = false; // this column is not editable
$col["align"] = "center"; // this column is not editable
$col["search"] = true; // this column is not searchable
$cols[] = $col;

$col = array();
$col["title"] = "Closed";
$col["name"] = "closed";
$col["width"] = "50";
$col["editable"] = true;
$col["edittype"] = "checkbox"; // render as checkbox
$col["editoptions"] = array("value"=>"Yes:No"); // with these values "checked_value:unchecked_value"
$col["searchoptions"] = array("defaultValue"=>'No');
$cols[] = $col;

# Custom made column to show link, must have default value as it's not db driven
$col = array();
$col["title"] = "Details";
$col["name"] = "view_more";
$col["width"] = "20";
$col["align"] = "center";
$col["search"] = false;
$col["sortable"] = false;
$col["link"] = "http://localhost/?id={id}"; // e.g. http://domain.com?id={id} given that, there is a column with $col["name"] = "id" exist
$col["linkoptions"] = "target='_blank'"; // extra params with <a> tag
$col["default"] = "View More"; // default link text
$cols[] = $col;

$g = new jqgrid();

// $grid["url"] = ""; // your paramterized URL — defaults to REQUEST_URI
$grid["rowNum"] = 10; // by default 20
$grid["sortname"] = 'id'; // by default sort grid by this field
$grid["sortorder"] = "desc"; // ASC or DESC
$grid["caption"] = "Invoice Data"; // caption of grid
$grid["autowidth"] = true; // expand grid to screen width
$grid["multiselect"] = true; // allow you to multi-select through checkboxes
$grid["persistsearch"] = true; // persist search settings on page reload

// initialize search, 'name' field equal to (eq) 'Client 1'
// operators: ['eq','ne','lt','le','gt','ge','bw','bn','in','ni','ew','en','cn','nc']
$sarr = <<< SEARCH_JSON
{
"groupOp":"AND",
"rules":[
{"field":"name","op":"cn","data":"Maria"},
{"field":"closed","op":"eq","data":"No"}
]
}
SEARCH_JSON;

$grid["search"] = true;
$grid["postData"] = array("filters" => $sarr );

// refresh page after search dialog submit to persist filters
$grid["search_options"]["onSearch"] = 'function () { setTimeout("location.reload();",500); }';

// export PDF file
$grid["export"] = array("format"=>"pdf", "filename"=>"my-file");

$g->set_options($grid);

$g->set_actions(array(
"add"=>true, // allow/disallow add
"edit"=>true, // allow/disallow edit
"delete"=>true, // allow/disallow delete
"rowactions"=>true, // show/hide row wise edit/del/save option
"export"=>true, // show/hide export to excel option
"autofilter" => true, // show/hide autofilter for search
"search" => "advance" // show single/multi field search condition (e.g. simple or advance)
)
);

// you can provide custom SQL query to display data
$g->select_command = "SELECT i.id, invdate , c.name,
i.note, i.total, i.closed FROM invheader i
INNER JOIN clients c ON c.client_id = i.client_id";

// this db table will be used for add,edit,delete
$g->table = "invheader";

// pass the cooked columns to grid
$g->set_columns($cols);

// generate grid output, with unique grid name as 'list1'
$out = $g->render("list1");
?>
=============================================================================

/* CONFIG.PHP */

<?php
$db_conf = array();
$db_conf["type"] = "mysqli";
$db_conf["server"] = "localhost"; // or your mysql ip
$db_conf["user"] = "root"; // username
$db_conf["password"] = ""; // password
$db_conf["database"] = "griddemo"; // database

// include and create object
$base_path = strstr(realpath("."),"demos",true)."lib/";
include($base_path."inc/jqgrid_dist.php");
$g = new jqgrid($db_conf);
$g->con->debug = 1; // changed from 0 to 1

?>