PHP SQL内部联接？

Question

So I'm making a portfolio website where I can post and edit blogs.

I'm making the blog edit page and I'm having trouble with combining two table together.

The first table is for the blogs and the second table holds all the different blog categories.

Here's how I'm getting the blog posts:

$qStr = "SELECT post_title, post_content, post_description, post_active, category_id  FROM posts WHERE post_id = {$post_id}";

Here's how I'm getting the blog categories:

$qStr = "SELECT category_name FROM categories WHERE category_id = {$category_id}";

So in my edit blog post page I have a dropdown box that I need to show which category that blog post is in, and be able to change it. I have a category_id in my blog table. My question is how do I get the dropdown to show which category the post is under?

Right now my drop down code looks like this (note: Right now I'm just populating the dropdown with all the categories)

<div class="form-group">
     <label for="categorySelect" class="col-lg-2 control-label">Category</label>
     <div class="col-lg-3">
          <select class="form-control" id="categorySelect">
                <?php
                     foreach ($categories as $cat) {
                         echo("<option>{$cat['category_name']}</option>");   
                     }
                 ?>
           </select>
     </div>
</div>

Answer 1

You need to set up the selected attribute for select (option) element, something like this:

<?php
    foreach ($categories as $cat) {
       if ($cat['category_name'] == $category_of_your_post)
           echo "<option selected=\"selected\">{$cat['category_name']}</option>"; 
       else  
           echo "<option>{$cat['category_name']}</option>"; 
    }
?>

BTW, I think that you have the wrong queries (if I understood correctly your question). Basically you need to retrieve the category_id of your post and perform an equality question against the array of categories:

$qStrBlog = "SELECT post_title, post_content, post_description, post_active, category_id  FROM posts WHERE post_id = {$post_id}";
$qStrCat = "SELECT category_id, category_name FROM categories";

And then:

<?php
    foreach ($categories as $cat) {
       if ($cat['category_id'] == $blog_data['category_id'])
           echo "<option selected=\"selected\">{$cat['category_name']}</option>"; 
       else  
           echo "<option>{$cat['category_name']}</option>"; 
    }
?>

Answer 2

You have two options:

Add a selected attribute with an if-condition in the foreach loop:

foreach ($categories as $cat) {
    echo '<option';
    if ($cat['category_id'] == $post['category_id']) echo ' selected';
    echo '>'.$cat['category_name'].'</option>';
}

Or use an INNER JOIN on the post SELECT query:

$qStr = "SELECT p.post_title, p.post_content, p.post_description, p.post_active, p.category_id, c.category_name FROM posts INNER JOIN categories c ON c.category_id = p.category_id WHERE post_id = {$post_id}";

and throw the first option element as the "default currently selected" option:

      <select class="form-control" id="categorySelect">
            <option value="<?= $post['category_id'] ?>"><?= $post['category_name'] ?> (current)</option>
            <?php
                 foreach ($categories as $cat) {
                     echo("<option>{$cat['category_name']}</option>");   
                 }
             ?>
       </select>

I've made the assumption that you've correctly loaded your result from the first SELECT query into $post . Note that if it's possible to not set a Category to a Post, you should use LEFT JOIN instead and wrap the first option element output contingent on $post['category_id'] not being empty.