whenever i use Where clasue in query, it is not working

i want to show some specific data by condition

i tried this below –
$query = “SELECT * FROM batch_details where ins_name=’safi’ “;
but when i use where clause in query it doesn`t work

//fetch.php

include('database_connection.php');

$column = array("id", "batch_student_name","student_marks");

$query = "SELECT * FROM `batch_details` ";

if(isset($_POST["search"]["value"]))
{
    $query .= '
    WHERE batch_student_name LIKE "%'.$_POST["search"]["value"].'%" ';
}

if(isset($_POST["order"]))
{
    $query .= 'ORDER BY '.$column[$_POST['order']['0']['column']].' '.$_POST['order']['0']['dir'].' ';
}
else
{
    $query .= 'ORDER BY id ASC ';
}

$query1 = '';

if($_POST["length"] != -1)
{
    $query1 = 'LIMIT ' . $_POST['start'] . ', ' . $_POST['length'];
}

$statement = $connect->prepare($query);

$statement->execute();

$number_filter_row = $statement->rowCount();

$result = $connect->query($query . $query1);

$data = array();

foreach($result as $row)
{
    $sub_array = array();
    $sub_array[] = $row['id'];
    $sub_array[] = $row['batch_student_name'];
    $sub_array[] = $row['student_marks'];
    
    $data[] = $sub_array;
}

function count_all_data($connect)
{
    $query = "SELECT * FROM `batch_details` ";

    $statement = $connect->prepare($query);

    $statement->execute();

    return $statement->rowCount();
}

$output = array(
    'draw'      =>  intval($_POST['draw']),
    'recordsTotal'  =>  count_all_data($connect),
    'recordsFiltered'   =>  $number_filter_row,
    'data'      =>  $data
);

echo json_encode($output);