php - 为什么此查询重复此代码中的名字和姓氏

Question

当我运行这个查询时，我得到了正确的结果，但名称和父亲的名字在所有行中重复。我只想要一次。例如，我输入 1773 身份证号码来测试它。

<?


                $query = mysql_query("
                                        SELECT *
                                        FROM students,grades,subjects
                                        WHERE
                                        students.id_students = grades.id_students AND 
                                        grades.id_subjects = subjects.id_subjects AND 
                                        students.id_students = 1773 ;




                                         ");

                while ($row = mysql_fetch_assoc($query)

                    ){
                    $id_students = $row['id_students'];
                    $firstname = $row['firstname'];
                    $surename = $row['surename'];
                    $father = $row['father'];
                    $marks = $row['marks'];
                    $class = $row['class'];
                    $name = $row['name'];


                 echo "$firstname" . "$surename"; 
                 echo "$marks" ." " . "$name" ; 
                 echo "<br>";
                 echo "$class";

                    }

?>

Answer 1

在 FROM 子句中仅使用一个表，其他表则使用 JOIN。

SELECT s.*, 
       g.*, 
       su.*
FROM students s
JOIN grades g
    ON g.id_students = s.id_students
JOIN subjects su
    ON su.id_subjects = g.id_subjects
WHERE s.id_students = 1773