JQuery AJAX post variable to custom php file in WordPress - ajax

Question

I was tried to make JQuery AJAX post variable to custom php file in WordPress. But it doesn't work at all.
$column_filter_text = $_POST['filtertext'];
Javascript success but returns undefined value. Actually the variable was not passing from JQuery AJAX to Php file. The following are the code below:
database-table-data.php in the WordPress theme folder.
<?php
require_once('../../../wp-config.php');
require_once("../../../wp-load.php");
global $wpdb;
$column_filter_text = $_POST['filtertext'];
echo "<script>console.log('php post variable: '" . $column_filter_text . ");</script>";
$result = $wpdb->get_results ("
SELECT " . $column_filter_text . " FROM wpgw_wpdatatable_1");
foreach ( $result as $row )
{
echo $row . "<br>";
$return_arr[] = array("filter_column_data" => $row);
}
echo json_encode($return_arr);
?>
Javascript file code:
columnfiltertext = "bmc";
jQuery.ajax({
url: "https://********.com/wp-content/themes/oceanwp/database-table-data.php",
method: "post",
//data: { "message":$('#input-message').val(),"sender":$('#sender').val(),"receiver":$('#receiver').val()},you can pass the values directly like this or else you can store it in variables and can pass
data: { filtertext: "bmc" }, //"column_filter_number":column_filter_number},
success: function(response){
var len = response.length;
for(var i=0; i<len; i++){
var filter_column_data = response[i].filter_column_data;
//alert(filter_column_data);
console.log(i + ":" + filter_column_data);
}
},
error: function() {
alert('Not OKay');
}
});
});
});

Answer 1

This is the right way to getting data from the database
Add this code to the function.php theme file
<?php
function database_table_data()
{
global $wpdb;
$column_filter_text = $_POST['column_filter_text'];
$result = $wpdb->get_results ("SELECT " . $column_filter_text . " FROM wpgw_wpdatatable_1");
if($result){
echo json_encode($result);
} else {
echo json_encode('record not fount');
}
wp_die();
}
add_action('wp_ajax_database_table_data', 'database_table_data');
add_action('wp_ajax_nopriv_database_table_data', 'database_table_data');
?>
Javascript file code:
<script>
(function ($) {
$('button').click(function (e) {
e.preventDefault();
var columnfiltertext = "bmc";
$.ajax({
type: "post",
url: "https://********.com/wp-admin/admin-ajax.php?action=database_table_data",
data: { column_filter_text: columnfiltertext },
dataType: "json",
success: function (response) {
console.log(response)
}
});
});
})(jQuery)
</script>