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

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

您可能必须使用 subquery为此。

$r2 = mysqli_query($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'");