PHP MySQL多个SQL查询或每个查询的JOIN

Question

If I have two tables with their respective columns:

=====================
product_categories
=====================
id | name
=====================

=======================
products
=======================
id | category_id | name
=======================

And I have the following PHP functions:

// Returns an array of all rows from the products
function getProducts() { ... } 

// returns the corresponding row to the given id of the product category
function getProductCategory($category_id) { ... } 

Currently, I am displaying a list of all products in a table with the following headings:

• id
• Category
• Name

Where category is the name of the category corresponding to the category_id of the product.

Currently I am using a foreach loop to iterate through the product and calling the getProductCategory(...) function for each product:

<?php
...

$products = getProducts();

foreach ($products as $product) {
    $product_category = getProductCategory($product['category_id']);
    ...
}

...
?>

Which would be an extensive amount of queries to the database if there are lots of products with many repeated queries.

Would it be good practice if the getProducts() function include all it's category information using a JOIN in the SQ L statement?

Answer 1

If you want to get id , category_name and product_name each time, you should make ONE method and avoid to make one select , then a foreach on each product and an other select to get all value.

So try something like this maybe :

function getProductsData() {

    $querie = 'SELECT 
                 p.id, p.name,
                 pc.name as Category
               FROM products as p
               LEFT JOIN product_categories as pc on pc.id = p.category_id
               ORDER BY p.name; -- optionnal
              ';

    // Get the data and return them
    // You should get an array with one row = 
    // id (of the product) / name (of the product) / Category (the name of the category)


}

Answer 2

Yes, Join will be better. It will reduce the number of queries for fetching the category. Otherwise, you can do the separate query for getting the categories as below code, but I will suggest Join.

$products = getProducts();
$categoryIds = [];
foreach ($products as $product) {
    $categoryIds[] = $product['category_id'];
    ...
}
$product_category = getProductCategory($categoryIds);

You have to modify the query in getProductCategory() and add where in condition for comparing category ID In getProductCategory() , you can implode the category IDs, for adding it into the where in clause.