php - 我的选择语句正确吗

Question

这个陈述在句法上是否正确:

$query = "SELECT matric_no session course_name
              FROM main_table session
              WHERE main_table.matric_no = '$_POST[matric_no]'
                  AND session.session_name = '$_SESSION[session]'
                  AND session.course_name =  '$_SESSION[course_name]'";
$result = mysql_query($query) ;                       
$duplicates = mysql_num_rows($result);

if ($duplicates = 1) {
    echo "you have dis in the database";
};

Answer 1

您不需要SELECT 中的所有信息来检查 session 是否在数据库中。

   $matricNo = $_POST[matric_no];
    $sessionName = $_ SESSION[session];
    $courseName = $_ SESSION[course_name];

//here you should use mysql_real_escape_string() for security
//like this $matricNo = mysql_real_escape_string($matricNo);

$query = "SELECT m.matric_no
          FROM main_table as m, session as s
          WHERE m.matric_no = '$matricNo' 
            AND s.session_name = '$sessionName'
            AND s.course_name = '$courseName'"; 

$result = mysql_query($query) or die (mysql_error()); 

$duplicates = mysql_num_rows($result); 

if ($duplicates > 0) { 
    echo "you have dis in the database"; 
};