可以使用foreach循环或implode

<?php

 if($_SERVER['REQUEST_METHOD']=='POST'){
  //Getting values 
 require_once('dbConnect.php');
 // i am assuming $con is your connection variable

 // its good practice to check against sql injection
 $courseList = mysqli_real_escape_string( $con, $_POST['courseList'] );
 $professor_ID = mysqli_real_escape_string( $con, $_POST['Prof_ID'] );

 $list = json_decode( $courseList );

 print_r( $list );

 // Assuming $list is 
 //   Array
 //  (
 //    [0] => 1
 //    [1] => 2
 //  )    

 foreach ( $list as $p_id ) {
   // prepare your query
   $sql = "select Stud_ID,student.f_Name,student.l_Name from student,course where course.S_ID = student.Stud_ID and course.P_ID = $p_id ";
   // execute and do other stuff
}

// or use implode
$pid = (implode(', ', $list);
$sql = "select Stud_ID,student.f_Name,student.l_Name from student,course where course.S_ID = student.Stud_ID and course.P_ID in $pid ";
// execute and do other stuff

?>

在这个代码片段中，我使用inflode函数将$list数组转换为逗号分隔的字符串，然后将其与SQL查询字符串连接起来。这应该可以正确地与您的SQL查询一起工作。

$implodedList = implode(', ', $list);

$sql = "select Stud_ID,student.f_Name,student.l_Name from student,course where course.S_ID = student.Stud_ID and course.P_ID in ($implodedList)";