将变量发送到bind_param错误

Question

我有这个查询我需要MYSQL查询忽略WHERE子句中的空变量并将发送变量发送到bind_param

这是代码

<?php
    /**
     * Created by PhpStorm.
     * User: YousefAltaf
     * Date: 11/1/2015
     * Time: 11:40 AM
     */

    //post vars
    $institute = $_POST['institute'];

    if (isset($_POST['sections'])) {
        $sections = $_POST['sections'];
    }

    if (isset($_POST['division'])) {
        $division = $_POST['division'];
    }

    if (isset($_POST['level'])) {
        $level = $_POST['level'];
    }

    //check empty var
    $where = "WHERE a.institute =?";
    $bind = "i";
    $prams = "$"."institute, ";
    if (!empty($sections)) {
        $where .= " AND a.section =?";
        $bind .= "i";
        $prams .= "$"."sections, ";
    }

    if (!empty($division)) {
        $where .= " AND a.division =?";
        $bind .= "i";
        $prams .= "$"."division, ";
    }

    if (!empty($level)) {
        $where .= " AND a.phase =?";
        $bind .= "i";
        $prams .= "$"."level";
    }

    //var_dump($institute, $sections, $division, $level);
    var_dump($bind);
    print_r ($prams);
    if ($getSearch = $db->prepare("SELECT
    a.*, a.id AS stud_id, b.id, b.ins_name, c.id, c.sec_name, d.id, d.div_name
    FROM student_basic_info AS a
    JOIN institutes AS b ON (a.institute = b.id)
    CROSS JOIN ins_sections AS c ON (a.section = c.id)
    CROSS JOIN ins_division AS d ON (a.division = d.id)
    $where GROUP BY a.id
    ")
    ) {

        $studSearch = array();
        $getSearch->bind_param('iii', $prams);

    } else {
        printf("Errormessage: %s\n", $db->error);
    }
    if ($getSearch->execute()) {
        $results = $getSearch->get_result();
        while ($vStud = mysqli_fetch_array($results)) {
            $studSearch[] = $vStud;
            ?>

得到了

  

警告：mysqli_stmt :: bind_param（）：类型中的元素数   定义字符串与绑定变量数不匹配