mysql如果count为null，则将其设为零

Question

How do I set the field most_popular to 0 if its count is null with a select statement inside a select statement

i've tried IFNULL(SELECT COUNT(*) ...), 0) as most_popular but it won't work and I tried COALESCE(SELECT COUNT(*) ...., 0) as 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

Try this,

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

or how about this, ( your current query )

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