Question

我有学校的mysql数据库有15个表（15个教室），每个表都有统一的字段/简单数据，如：ID，DATE，TIME，CLASSROOM_NO，STUDENTS_ALL，STUDENTS_CURRENT，COMMENTS

方法是能够通过增加db的php格式不断更新这些数据，没关系，工作正常。

在另一个php页面中，我有display.php，它只显示我添加的最新记录，所以我可以知道对这个教室做的最新更新，这也很好，这正是我需要的，这是我的代码：

<?php
$con=mysqli_connect("localhost","classroom","mypsassword","mysqluser");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$result = mysqli_query($con,"SELECT id, date, time, classroom_no, students_all,     student_current,comments FROM classroom_1 ORDER BY id DESC LIMIT 1");


while($row = mysqli_fetch_array($result))
 {

 echo "<b>Room:</b> " . $row['classroom_no'] . "<br>";
 echo "<b>All students:</b> " . $row['students_all'] . "<br>";
 echo "<b>Available students:</b> " . $row['students_current'] . "<br>";
 echo "<b>Absent:</b> ";
 echo floatval($row['students_all'])  -  floatval($row['students_current']);
 echo "<br>";
 echo "<b>Updated on:</b> " . $row['date'] ."<br>";
 echo "<b>Update time:</b> " . $row['time']."<br>" ;

  }

mysqli_close($con);

?>

现在，我在一个页面中实现和检索每个教室的最新更新没有任何问题......我所挣扎的是从每个表中选择最新记录，然后在同一页面中相应地显示它们。所以要有一个php页面说all_classrooms.php

并在一个页面中显示所有教室（仅来自每个表的最新记录更新），因此我无法理解如何在同一时间从所有表中选择sql查询并将其限制为最新记录...

我的表是这样的顺序命令： classroom_1 classroom_2 classrrom_3

请告知

Answer 1

正如Kickstart建议的那样：我建议您规范化数据库设计。将所有课堂数据放入一个带有列的表中，以显示任何特定行所关联的教室。

我不会重新考虑的其他（变通方法）解决方案是create a view。看起来像是

CREATE VIEW allData AS
SELECT * from Classroom1
UNION ALL SELECT * from Classroom2
....

然后从此视图中选择select。

Answer 2

最好重新设计数据库，其中一个用于教室，另一个用于课程（每个教室有许多行），等等。

但是，如果不可能，你需要这样的东西： -

SELECT classroom, id, date, time, classroom_no, students_all, student_current, comments
FROM
(
    SELECT '1' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_1
    UNION
    SELECT '2' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_2
    UNION
    SELECT '3' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_3
    UNION
    SELECT '4' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_4
    UNION
    SELECT '5' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_5
    UNION
    SELECT '6' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_6
    UNION
    SELECT '7' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_7
    UNION
    SELECT '8' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_8
    UNION
    SELECT '9' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_9
    UNION
    SELECT '10' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_10
    UNION
    SELECT '11' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_11
    UNION
    SELECT '12' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_12
    UNION
    SELECT '13' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_13
    UNION
    SELECT '14' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_14
    UNION
    SELECT '15' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_15
) Sub1
INNER JOIN
(
    SELECT classroom, MAX(id) AS maxid
    FROM
    (
        SELECT '1' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_1
        UNION
        SELECT '2' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_2
        UNION
        SELECT '3' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_3
        UNION
        SELECT '4' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_4
        UNION
        SELECT '5' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_5
        UNION
        SELECT '6' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_6
        UNION
        SELECT '7' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_7
        UNION
        SELECT '8' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_8
        UNION
        SELECT '9' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_9
        UNION
        SELECT '10' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_10
        UNION
        SELECT '11' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_11
        UNION
        SELECT '12' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_12
        UNION
        SELECT '13' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_13
        UNION
        SELECT '14' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_14
        UNION
        SELECT '15' AS classroom, id, date, time, classroom_no, students_all, student_current, comments FROM classroom_15
    ) Sub3
    GROUP BY classroom
) Sub2
ON Sub1.classroom = Sub2.classroom AND Sub1.id = Sub2.maxid

请注意，我在UNION中添加了固定的教室列。这可能会复制classroom_no的值。

还有一个名为students_all的列。这表明您有一个包含学生列表的列。如果是这样的话，最好把它拆分成另一个表，每个表可以有很多行（一个班级每个学生一个）

从一个数据库中的多个表中选择最新记录（MYSQL PHP）

2 个答案: