Question

我有两个查询应该返回我的DB中相对于当前行的下一行和上一行。

然而，它们都返回相同的东西，下一行，并且由于某种原因，第二个查询也返回一个空数据集。

代码：

<?php

    // Credentials
    $dbhost = "localhost";
    $dbname = "buildingcodes";
    $dbuser = "***";
    $dbpass = "***";

    global $tutorial_db;

    $tutorial_db = new mysqli();
    $tutorial_db->connect($dbhost, $dbuser, $dbpass, $dbname);
    $tutorial_db->set_charset("utf8");

    //  Check Connection
    if ($tutorial_db->connect_errno) 
    {
        printf("Connect failed: %s\n", $tutorial_db->connect_error);
        exit();
    }


    $id = 'R401.4 Soil tests.'; //$_GET['id'];

    echo 'id: ' . $id;
    echo '</br>';

    //////

    $query = "SELECT * FROM codes WHERE subsection > '". $id ."' ORDER BY subsection LIMIT 1";

    $result = $tutorial_db->query($query);  

    while($results = $result->fetch_array()) 
    {
        $result_array[] = $results;
    }


    echo '</br></br>';

    if (isset($result_array)) 
    {
        foreach ($result_array as $result) 
        {
            echo 'first q: ' . $result['subsection'];
            echo '</br>';   
        }
    }   



    /////


    $query = "SELECT * FROM codes WHERE subsection < '". $id ."' ORDER BY subsection LIMIT 1";

    $result = $tutorial_db->query($query);

    while($results = $result->fetch_array()) 
    {
        $result_array[] = $results;
    }


    echo '</br>';

    if (isset($result_array)) 
    {
        foreach ($result_array as $result) 
        {
            echo 'second q: ' . $result['subsection'];
            echo '</br>';   
        }
    }   

?>

输出：

id: R401.4 Soil tests.

first q: R401.4.1 Geotechnical evaluation.

second q: R401.4.1 Geotechnical evaluation.
second q:

但是应该输出：

id: R401.4 Soil tests.

    first q: R401.4.1 Geotechnical evaluation.

    second q: R401.3 Drainage.

从这组数据中 DB Screen Shot

为什么这不会返回前一行？

Answer 1

你可以尝试一下吗？你可以在这里测试一下http://www.sqlfiddle.com/#!2/e2881/1

SELECT * from ss where subsection > 'R401.4 Soil tests'
ORDER BY SUBSTRING_INDEX(subsection, ' ', 1) ASC;
+-------------------------+
| subsection              |
+-------------------------+
| R401.4.1 Geotech.       |
| R401.4.2 Compressible   |
| R402.1 Wood foundations |
+-------------------------+
3 rows in set (0.00 sec)

SELECT * from ss where subsection < 'R401.4 Soil tests'
ORDER BY SUBSTRING_INDEX(subsection, ' ', 1) DESC;
+---------------------+
| subsection          |
+---------------------+
| R401.3 Drainage     |
| R401.2 Requirements |
| R401.1 Application  |
+---------------------+
3 rows in set (0.01 sec)

当subsection之间dot(.)之间的查询超过两位时，查询将无效。然后可能以下查询适用于NEXT子部分。

    ORDER BY LENGTH(SUBSTRING_INDEX(subsection, ' ', 1)),
        SUBSTRING_INDEX(subsection, ' ', 1) ASC;

但不确定是否为PREV小组工作。

为什么我的两个不同的问题会回归同样的问题？

1 个答案: