SELECT
ProductName, ProductImages, ProductDescription,
ProductPrice, ProductAddDate, cSchema_Name, cValueValue
  FROM
Product p INNER JOIN CharacteristicsValue cv
ON p.ID_product = cv.cValueProduct_FK
INNER JOIN CharacteristicsSchema cs
ON cv.cValueSchema_FK = cs.ID_cSchema
  WHERE
ProductUrl = ?
AND cv.cValueSchema_FK = cs.ID_cSchema
AND cs.cSchema_Category_FK = p.ProductCategory_FK");

"SELECT ProductName, ProductImages, ProductDescription,
        ProductPrice, ProductAddDate, ID_product, ProductCategory_FK
 FROM Product
 WHERE ProductUrl = ?"

"SELECT cSchema_Name, cValueValue
 FROM CharacteristicsValue cv
 JOIN CharacteristicsSchema cs ON cv.ID_cValue = cs.ID_cSchema
 WHERE cv.cValueProduct_FK = ? AND cs.cSchema_Category_FK = ?"

$stmt = $tmp_conn->prepare("SELECT ProductName, ProductImages, ProductDescription,
            ProductPrice, ProductAddDate, ID_product, ProductCategory_FK
            FROM Product
            WHERE ProductUrl = ?");
    $stmt->bind_param('s', $url);
    $stmt->execute();
    $result = $stmt->get_result();
    while ($row = $result->fetch_assoc()) {
        array_push($data, $row);
    }
    $result->free_result();

    $id_prod = $data[0]['ID_product'];
    $id_category = $data[0]['ProductCategory_FK'];

    $stmt = $tmp_conn->prepare("SELECT cSchema_Name, cValueValue
            FROM CharacteristicsValue cv
            INNER JOIN CharacteristicsSchema cs ON cv.ID_cValue = cs.ID_cSchema
            WHERE cv.cValueProduct_FK = ? AND cs.cSchema_Category_FK = ?");
    $stmt->bind_param('ii', $id_prod, $id_category);
    $stmt->execute();
    $result = $stmt->get_result();
    while ($row = $result->fetch_assoc()) {
        array_push($data, $row);
    }
    $result->free_result();

SELECT
ID_product, ProductName, ProductImages, ProductDescription,
ProductPrice, ProductAddDate, cSchema_Name, cValueValue
FROM
Product p INNER JOIN CharacteristicsValue cv
ON p.ID_product = cv.cValueProduct_FK
INNER JOIN CharacteristicsSchema cs
ON cv.cValueSchema_FK = cs.ID_cSchema
WHERE
ProductUrl = ?
AND cv.cValueSchema_FK = cs.ID_cSchema
AND cs.cSchema_Category_FK = p.ProductCategory_FK")
GROUP BY `ID_product`;