php - 在 PHP 中输​​出 MySQL LEFT JOIN

Question

我做了这样一个mysql查询

SELECT 
    forum_subcategories.name_sub, 
    forum_categories.id, 
    forum_categories.name 
FROM 
forum_subcategories 
LEFT JOIN forum_categories ON forum_subcategories.catid = forum_categories.id

当我这样回应时

while($row = $result->fetch_assoc()){
echo '<h3><strong>'.$row['name'].' - '.$row['id'].'</strong></h3>';
echo '<h4>'.$row['name_sub'].' - '.$row['id'].'</h4>';

我得到以下结果:

Category-1
subcategory belonging to 1

Category-1
subcategory belonging to 1

Category-2
subcategory belonging to 2

Category-2
subcategory belonging to 2

Category-3
subcategory belonging to 3

Category-3
subcategory belonging to 3

但是我要找的结果是这样的:

Category-1
subcategory belonging to 1
subcategory belonging to 1

Category-2
subcategory belonging to 2
subcategory belonging to 2

Category-3
subcategory belonging to 3
subcategory belonging to 3

我将如何实现这个结果？

Answer 1

您的查询实际上是正确的，这只是仅在类别发生更改时将其作为输出发送的问题。将类别存储在变量中，并在每次循环迭代时检查新值是否与旧值匹配。如果没有，打印出来。

// variable to hold the current one...
// It starts empty.
$current_category = '';
// Remember whether there's a <div> unclosed
$subcat_div_open = false;

while($row = $result->fetch_assoc()){
  // Compare to the category of the loop iteration
  if ($row['name'] !== $current_category) {
    // If there's a subcategory <div> open, close it
    if ($subcat_div_open) {
       echo '</div>';
    }
    echo '<h3><strong>'.$row['name'].' - '.$row['id'].'</strong></h3>';
    // Store the new one to compare next time around
    $current_category = $row['name'];
    // Ouput an opening <div> for the subcategories
    // and keep track of its state
    echo '<div>';
    $subcat_div_open = true;
  }
  // Always output the subcategory
  echo '<h4>'.$row['name_sub'].' - '.$row['id'].'</h4>';
}
// Clean up the open div
if ($subcat_div_open) echo '</div>';