MySQL - Select 一次查询中来自不同表的多行

Question

I have 2 tables "products" and "products_images"., I want to load each product with it's images in the same query and then json_encode then send it to front end.

products table
+----+----------------+-------+
| id | product_name   | price |
+----+----------------+-------+
| 1  | product name 1 | 15    |
+----+----------------+-------+
| 2  | product name 2 | 23.25 |
+----+----------------+-------+
| 3  | product name 3 | 50    |
+----+----------------+-------+


product_images table
+----+------------+-----------------------------------------------------+
| id | product_id | image                                               |
+----+------------+-----------------------------------------------------+
| 1  | 1          | e5j7eof75y6ey6ke97et5g9thec7e5fnhv54eg9t6gh65bf.png |
+----+------------+-----------------------------------------------------+
| 2  | 1          | sefuywe75wjmce5y98nvb7v939ty89e5h45mg5879dghkjh.png |
+----+------------+-----------------------------------------------------+
| 3  | 1          | 7u5f9e6jumw75f69w6jc89fwmykdy0tw78if6575m7489tf.png |
+----+------------+-----------------------------------------------------+

I want the query to return this

{
  id: 5,
  product_name: 'product name 1',
  price: 25.23,
  images: [
   {
    id: 1,
    image: 'e5j7eof75y6ey6ke97et5g9thec7e5fnhv54eg9t6gh65bf.png'
   },
   {
    id: 2,
    image: 'sefuywe75wjmce5y98nvb7v939ty89e5h45mg5879dghkjh.png'
   },
  ]
}

What I do is I make a loop on each product in php and then load it's images, but I don't believe this is the best solution or the best performance.

Answer 1

/**
 * Results from a SELECT * FROM products query
 */
$products = [
  [
    'id' => 1,
    'product_name' => 'product name 1',
    'price' => 15,
  ],
  [
    'id' => 2,
    'product_name' => 'product name 2',
    'price' => 23.25,
  ],
  [
    'id' => 3,
    'product_name' => 'product name 3',
    'price' => 50,
  ],
];

/**
 * Results from either
 * SELECT * FROM images
 * or
 * SELECT * FROM images WHERE product_id IN (?,?,?, ...) <- product ids
 */
$images = [
  [
    'id' => 1,
    'product_id' => 1,
    'e5j7eof75y6ey6ke97et5g9thec7e5fnhv54eg9t6gh65bf.png'
  ],
  [
    'id' => 2,
    'product_id' => 1,
    'sefuywe75wjmce5y98nvb7v939ty89e5h45mg5879dghkjh.png'
  ],
  [
    'id' => 3,
    'product_id' => 1,
    '7u5f9e6jumw75f69w6jc89fwmykdy0tw78if6575m7489tf.png'
  ],
];

foreach ($products as $i => $product) {
  $products[$i]['images'] = array_filter($images, function ($image) use ($product) {
    return $image['product_id'] === $product['id'];
  });
}

var_export($products);

Answer 2

SELECT p.product_id, i.image_png, ...
    FROM products AS p
    JOIN images AS i   ON i.product_id = p.product_id
    WHERE ...
    ORDER BY ...

Then, in a loop

echo "<img src='...$image_png ...'>";

add an "anchor" if you want the images to be clickable. Add descriptive info if desired.

I see no need for json.

If you are "filtering", it is usually more efficient to build that into the SELECT statement.