nested loop but avoiding the repetition of first loop

Question

I have two tables; One is category and the other one is sub_category.

First I want to display all the items in category and store the value of each category and then display all the sub_categories related to that category but the category should not repeat (it should be displayed only once for all sub-categories).

.

<?php 
    $abcd = $mysqli->query("SELECT * FROM categories;");
    while($obj = $abcd->fetch_object())
    {
        $category = $obj->name;
        $results = $mysqli->query("SELECT * FROM `sub-category` WHERE category = '$category';");
        while($omg=$results->fetch_object())
        {
            echo $category. ' '.$omg->subcategory.'<br>';
        }
        echo $omg->subcategory;
    }
?>

change your categories query to something like SELECT * FROM DISTINCT categories — Ahad
– Ahad, Commented Jan 5, 2017 at 17:36
and learn some sql, it is very powerful skill to write great software, and it is very easy learn w3schools.com/sql/default.asp — Ahad
– Ahad, Commented Jan 5, 2017 at 17:37
@xFighter That will not work. Trivially, there can be multiple subcategories for each category. The categories relation already contains unique categories. — user2864740
– user2864740, Commented Jan 5, 2017 at 17:37
@xFighter That seems like reasonable output. Perhaps displayed like a tree. Moving the print of the (parent) category out of the inner loop would address that. Using a single SQL query would be an even bigger improvement - and teach additional concepts the OP may not be familiar with. — user2864740
– user2864740, Commented Jan 5, 2017 at 17:46

WEBjuju · Accepted Answer · 2017-01-05 18:02:39Z

1

Create an array of subcats and implode them so you only get commas where you want them. Only print the $category outside the loop.

<?php 
    $abcd = $mysqli->query("SELECT * FROM categories ");
    while ($obj = $abcd->fetch_object()) {                   
      $category = $obj->name;
      $results = $mysqli->query("SELECT * FROM `sub-category` WHERE category = '$category' ");     

       echo $category.': ';

       $subcats = array();
       while ($omg = $results->fetch_object()) {
         $subcats[] = $omg->subcategory;
       }

       echo implode(',', $subcats).'<br>';
    }
?>

answered Jan 5, 2017 at 18:02

WEBjuju

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JBES · Accepted Answer · 2017-01-05 20:43:22Z

0

Use a simple JOIN.

<?php 
    $abcd = $mysqli->query('SELECT DISTINCT categories.name,sub-category.subcategory FROM `categories` JOIN `sub-category` ON category.name = categories.category;');
    while($obj = $abcd->fetch_object())
    {
        echo $obj->name.' '.$obj->subcategory.'<br>';
    }
?>

edited Jan 5, 2017 at 20:43

answered Jan 5, 2017 at 17:56

JBES

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