我如何在查询$ r2中使用变量表$ r1而不是php文件中的FROM子句上的表名

Question

$r1 = mysqli_query($con,"SELECT course_id,status FROM attendance WHERE stud_id = '$stud_id'");

$r2 = mysqli_query($con,"SELECT course_name,status FROM **$r1** NATURAL JOIN course WHERE stud_id = '$stud_id'");

Answer 1

You may have to use subquery for this.

$r2 = mysqli_query($con,"SELECT course_name,status FROM 
        (SELECT course_id,status FROM attendance WHERE stud_id = '$stud_id') 
        NATURAL JOIN course WHERE stud_id = '$stud_id'");