寻找使MYSQL JOIN与关系表和全局变量一起使用的解决方案

Question

EDIT: The following code shows the answer to the question. thanks go to VolkerK.

$result = mysqli_query($link,"SELECT ctas.*, ctas_pr.*, nav.id
                              FROM web_ctas AS ctas

                              LEFT JOIN web_ctas_page_relation AS ctas_pr
                              ON ctas.id = ctas_pr.cta_id

                              LEFT JOIN web_navbar  AS nav
                              ON ctas_pr.navbar_id = nav.id
                              AND nav.link_name = '".$page."'")

                              or die(mysqli_error($link)
                      );

Good morning/afternoon/evening,

I am hoping some of you can help me out with a specific problem regarding mySQL.

I am trying to JOIN two tables pass some logic and get back the relevant field data for a match, I shall have to explain the process and the tables so you can garner a modicum of understanding of the code and processes.

The "web_ctas" table has a relational field that corresponds with the web_navbar table.

Massive thank you in advance to anyone who can help on this matter.

Below are the two tables:

web_ctas

id | title | img_src | img_alt | link_href | link_title | desc
==============================================================
1  | title | pears   | apples  | foo       | bar        | blah
2  | title | apples  | pears   | bar       | foo        | bleh

web_navbar

id | link_name | visible
========================
1  | home      |   1
2  | products  |   1

web_ctas_page_relation

id | cta_id | navbar_id
=======================
1  |    1   |    2
2  |    2   |    2

Below is the SQL I have thus far (I know this probably wont even work):

$query = mysqli_query($link,"SELECT web_ctas.*, web_navbar.id AS nav_id
                             FROM web_ctas
                             JOIN web_navbar
                             ON web_navbar.id = web_ctas.page_relation
                             AND page_relation='".$page."'");

Below is the HTML/PHP which will pull back the data from the SQL query results.

$page = 'home';

while($row = mysqli_fetch_object($query)): ?>
        <li>
            <a href="<? echo $row->link_href; ?>" title="<? echo $row->link_title; ?>">
                <h3><? echo $row->title; ?></h3>
                <div>
                    <img src="<? echo $row->img_src; ?>" alt"<? echo $row->img_alt; ?>">
                </div>
            </a>
        </li> <?
    endwhile;

So in a nutshell what I am looking for is a way in which to get the link_name field from the web_navbar table when it matches a row in web_ctas which has the relational id within the page_relation field and matches the variable $page.

If I have missed any key code/info please let me know.

Answer 1

Sorry, got to go; only time for an example script but not for an explaination. Since you already figured out the relation-table thingy yourself only given the 1NF link I'm confident you will be able to dig through this one as well ;-)
Works the same way using mysqli instead of pdo_mysql.

<?php
$pdo = new PDO('mysql:host=localhost;dbname=test;charset=utf8', 'localonly', 'localonly');
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
setup($pdo);

$navbar = 'nav_36'; // this would be $navbar='products'; in your case
$stmt = $pdo->prepare('
    SELECT
        nv.id as navid,
        nv.link_name,
        ct.id as ctasid,
        ct.title,
        ct.link_href
    FROM 
        tmp_web_navbar as nv
    LEFT JOIN
        tmp_web_ctas_nav_rel as r
    ON
        nv.id = r.id_navbar
    LEFT JOIN
        tmp_web_ctas as ct
    ON
        r.id_ctas=ct.id
    WHERE
        nv.link_name = ?
');
$stmt->setFetchMode(PDO::FETCH_ASSOC);
$stmt->execute(array($navbar));
foreach($stmt as $row ) {
    foreach($row as $k=>$v) {
        echo $k,'=', $v, ' ';
    }
    echo "\n";
}

// boilerplate for creating table layout and populating some example data
function setup($pdo) {
    $pdo->exec('
        CREATE TEMPORARY TABLE tmp_web_navbar (
            id int auto_increment,
            link_name varchar(32),
            visible varchar(32),
            primary key(id)
        )
    ');
    // add some entries to tmp_web_navbar since the example data uses the range [1,50]
    $stmt = $pdo->prepare('INSERT INTO tmp_web_navbar (link_name,visible) VALUES (?,?)');
    for($i=1; $i<60; $i++) {
        $stmt->execute(array(sprintf('nav_%02d', $i), 'title'));
    }

    $pdo->exec('
        CREATE TEMPORARY TABLE tmp_web_ctas (
            id int auto_increment,
            title varchar(32),
            link_href varchar(32),
            primary key(id)
        )
    ');
    // add some ctas elements
    $stmt = $pdo->prepare('INSERT INTO tmp_web_ctas (title,link_href) VALUES (?,?)');
    for($i=1; $i<60; $i++) {
        $stmt->execute(array('title', sprintf('ctas_%02d', $i)));
    }

    $pdo->exec("INSERT INTO tmp_web_ctas (title,link_href) VALUES
        ('title','foo'),
        ('title ','bar')
    ");

    // a table to store the relationships
    $pdo->exec('
        CREATE TEMPORARY TABLE tmp_web_ctas_nav_rel (
            id int auto_increment,
            id_ctas int,
            id_navbar int,
            primary key(id),
            key(id_ctas)
        )
    ');

    // and define some relationships
    // three of them having id_navbar=36: cats=4,5 and 7
    $stmt = $pdo->prepare('INSERT INTO tmp_web_ctas_nav_rel (id_ctas,id_navbar) VALUES (?,?)');
    $rel = array(
        1=>array(1,6,10,50),
        2=>array(2,13,15,30),
        3=>array(9,7,11,51),
        4=>array(17,24,36,34), // here
        5=>array(18,24,36,35), // here
        6=>array(19,24,33,38),
        7=>array(19,24,32,36), // and here
        8=>array(19,24,39,38),
    );
    foreach($rel as $ctas=>$navrels) {
        foreach( $navrels as $nav ) {
            $stmt->execute(array($ctas,$nav));
        }
    }
}

Answer 2

$query = mysqli_query($link,"SELECT web_ctas.*, web_navbar.id AS nav_id
                             FROM web_ctas
                             JOIN web_navbar
                             ON web_navbar.id IN (web_ctas.page_relation)
                             AND page_relation='".$page."'");