的MySQL如果計數爲null，則使零

Question

如何設置現場most_popular爲0;如果其計數爲null SELECT語句

我試過IFNULL（SELECT COUNT（*）內的select語句。 ..），0）作爲most_popular，但它不會工作，我嘗試 COALESCE（SELECT COUNT（*）......，0）作爲most_popular

$stmt = $db->prepare("SELECT *,   
    i.medium_image, i.width, i.height, 
    (SELECT COUNT(*) FROM order_details od WHERE od.product_id = p.product_id) as most_popular 

    FROM products p 
     INNER JOIN product_images i on i.product_id = p.product_id  
    WHERE p.department_id=:department_id AND p.is_active=1 
    $orderby   
    LIMIT :limit OFFSET :offset"); 

Answer 1

試試這個，

SELECT *, 
     i.medium_image, 
     i.width, 
     i.height, 
     COALESCE(s.totalCount, 0) most_popular 
FROM products p 
     INNER JOIN product_images i 
      ON i.product_id = p.product_id 
     LEFT JOIN 
     (
      SELECT product_id, Count(*) totalCount 
      FROM order_details 
      GROUP BY product_id 
     ) s ON s.product_id = p.product_id 
WHERE p.department_id = :department_id 
     AND p.is_active = 1 
$orderby 
LIMIT :limit OFFSET :offset 

或這個怎麼樣，（您當前的查詢）

COALESCE((SELECT COUNT(*) 
      FROM order_details od 
      WHERE od.product_id = p.product_id), 0) as most_popular