PHP MYSQL联合查询

Question

Im new to mysql queries and im having trouble obtaining the data structure I want. Im hoping one of you guys can help.

I have the following query:

SELECT *
FROM wp_postmeta
WHERE post_id IN (SELECT id from wp_posts WHERE post_type = 'product')

Which simply grabs all the data from Table 2 that has the same id as the product in Table 1. The problem is that the results return as:

{meta_id: "37230", post_id: "2549", meta_key: "total_sales", meta_value: "0"}
{meta_id: "37231", post_id: "2549", meta_key: "_virtual", meta_value: "no"}
{meta_id: "37232", post_id: "2549", meta_key: "_tax_status", meta_value: "taxable"}
{meta_id: "37233", post_id: "2549", meta_key: "_visibility", meta_value: "visible"}
{meta_id: "37234", post_id: "2549", meta_key: "_featured", meta_value: "no"}
{meta_id: "37235", post_id: "2549", meta_key: "_weight", meta_value: "0.50"}
{meta_id: "37236", post_id: "2549", meta_key: "_sku", meta_value: "HCS-DGMP"}
{meta_id: "37237", post_id: "2549", meta_key: "_product_attributes", meta_value: "a:0:{}"}
{meta_id: "37238", post_id: "2549", meta_key: "_regular_price", meta_value: "18.99"}
{meta_id: "37239", post_id: "2549", meta_key: "_sale_price", meta_value: ""}

As you can see, they all have the same post ID, but are returned in seperate objects. How can I modify my query above so that all of that returns in one object? I'll also be removing the meta_id as it is useless.

Answer 1

Since MySQL 5.7.22 you can use JSON_OBJECTAGG(key, value):

SELECT post_id, JSON_OBJECTAGG(meta_key, meta_value) AS meta_data
FROM wp_postmeta
WHERE post_id IN (SELECT id from wp_posts WHERE post_type = 'product')
GROUP by post_id

This will return meta_data as JSON_OBJECT with key: value pairs:

post_id | meta_data
   2549 | {"_sku": "HCS-DGMP", "_weight": "0.50", "_virtual": "no", "_featured": "no", "_sale_price": null, "_tax_status": "taxable", "_visibility": "visible", "total_sales": "0", "_regular_price": "18.99", "_product_attributes": "a:0:{}"}

Demo

If your server doesn't support JSON_OBJECTAGG(), I would use a PHP solution:

$postIds = array_unique(array_column($dbResult, 'post_id'));

$posts = [];
foreach ($postIds as $id) {
    $posts[$id] = (object)['id' => $id];
}

foreach ($dbResult as $row) {
    $posts[$row->post_id]->{$row->meta_key} = $row->meta_value;
}

echo json_encode(array_values($posts), JSON_PRETTY_PRINT);

Result:

[
    {
        "id": "2549",
        "total_sales": "0",
        "_virtual": "no",
        "_tax_status": "taxable",
        "_visibility": "visible",
        "_featured": "no",
        "_weight": "0.50",
        "_sku": "HCS-DGMP",
        "_product_attributes": "a:0:{}",
        "_regular_price": "18.99",
        "_sale_price": ""
    }
]

Demo

As long as you are not processing thousands of rows, I wouldn't worry about performance.