Question

在SQL中，如果record为null，如何显示0？

select sales_id, totalbuy, totalsell, totalbuy + totalsell as total from
(select sales_id, SUM(CASE WHEN side= 'buy' THEN 1 ELSE 0 END) AS totalbuy, 
SUM(CASE WHEN side= 'sell' THEN 1 ELSE 0 END) AS totalsell 
from car_orders 
where sales_id in ('sales1', 'sales2', 'sales3', 'sales4')only
GROUP BY sales_id)q
order by total desc
limit 0, 10;

car_orders之后我尝试插入*（car_orders + ISNULL（car_orders，0）），但收到错误。

Answer 1

使用+时，两个参数必须属于同一类型。我无法从您的问题中了解car是什么，但我认为它与0不兼容。

在这些情况下最好使用CONCAT。

CONCAT(car, IFNULL(car_orders, 0))

如果car_orders是表格，则此处无效 - 您必须使用列，即car_orders.MyColumn

如何使用IFNULL

我认为你不能在这里得到一个null，鉴于你的查询，买你会像这样使用IFNULL：

SELECT 
    sales_id,
    IFNULL(totalbuy, 0),
    IFNULL(totalsell, 0),
    IFNULL(totalbuy, 0) + IFNULL(totalsell, 0) as total
FROM
(
    SELECT
        sales_id,
        SUM(CASE WHEN side = 'buy' THEN 1 ELSE 0 END) AS totalbuy, 
        SUM(CASE WHEN side = 'sell' THEN 1 ELSE 0 END) AS totalsell 
    FROM
        car_orders 
    WHERE
        sales_id in ('sales1', 'sales2', 'sales3', 'sales4')
    GROUP BY
       sales_id
) q
ORDER BY total DESC
LIMIT 0, 10;

Answer 2

根据Sohnee的回答构建，这是我认为你想要使用的SQL：

SELECT 
    sales_id,
    IFNULL(totalbuy, 0),
    IFNULL(totalsell, 0),
    IFNULL(totalbuy, 0) + IFNULL(totalsell, 0) as total
FROM
(
    SELECT
        sid as sales_id,
        SUM(CASE WHEN side = 'buy' THEN 1 ELSE 0 END) AS totalbuy, 
        SUM(CASE WHEN side = 'sell' THEN 1 ELSE 0 END) AS totalsell 
    FROM 
        ( SELECT 'sales1' as sid UNION SELECT 'sales2' UNION SELECT 'sales3' UNION SELECT 'sales4' ) mysalesids
    LEFT OUTER JOIN car_orders
      ON sales_id = sid
    GROUP BY
       sales_id
) q
ORDER BY total DESC
LIMIT 0, 10;

以上的关键是“LEFT OUTER JOIN”。如果您可以在自己的表中使用'sales1'，'sales2'，'sales3'值，那么这将更可取，而不是进行子选择。

希望这有帮助，

...约翰

sql如果null显示0

2 个答案: