如何在单个保存按钮上运行多个查询？

When I click on the save button only all_university table updates but the all_colleges table has not been updated. How can I update two tables on one save button?

<?php
  if(isset($_POST['save'])) {
    $chk = implode(",", $_POST['company_name']);  
    $sql = "update all_university set placement = '$chk' where university_name = '".$_POST['university_name']."'";
    $sql = "update all_colleges set placement = '$chk' where college_name = '".$_POST['college_name']."'";
    $value = mysqli_multi_query($link,$sql);
    if($value == true){
        $msg .="<h5 style='color:green'>Successfull</h5>";
    } else {
        $msg .="<h5 style='color:red'>Error!</h5>";
    }
  }
?>

If you want to use the multi-query function, you have to concatenate the two query strings:

$sql = "update all_university set placement = '$chk' where university_name = '".$_POST['university_name']."';";
$sql .= "update all_colleges set placement = '$chk' where college_name = '".$_POST['college_name']."'";

And then execute mysqli_multi_query.

Or, as Rory already mentioned, just query twice using the normal mysqli_query function.

But you should really look into prepared statements as you are vulnerable to SQL injection!

It doesn't matter how many queries you have. Just run them all one by one.
Besides, you should be using prepared statements.

<?php
if(isset($_POST['save'])) {
    $chk = implode(",", $_POST['company_name']);  

    $sql = "update all_university set placement = ? where university_name = ?";
    $stmt = $link->prepare($sql);
    $stmt->bind_param("ss", $chk, $_POST['university_name']);
    $stmt->execute();

    $sql = "update all_colleges set placement = ? where college_name = ?";
    $stmt = $link->prepare($sql);
    $stmt->bind_param("ss", $chk, $_POST['college_name']);
    $stmt->execute();

    $msg .="<h5 style='color:green'>Successfull</h5>";
}

DO NOT use mysqli_multi_query(). It will do you no good and won't work the way you think.

Separate both query with semicolon (;)

$sql = "update all_university set placement = '$chk' where university_name = '".$_POST['university_name']."';";
$sql = "update all_colleges set placement = '$chk' where college_name = '".$_POST['college_name']."'";

Then, Append Both Query.

$sql = "update all_university set placement = '$chk' where university_name = '".$_POST['university_name']."'";
$sql .= "update all_colleges set placement = '$chk' where college_name = '".$_POST['college_name']."'";

Execute it.

$value = mysqli_multi_query($link,$sql);

The mysqli_multi_query() function performs one or more queries against the database. The queries are separated with a semicolon.