mysql - 如何在 SQL 选择中写入正确的 ORDER BY ... DESC？

Question

再会。

在此处检查表的结构。

我想选择：

select `idn` order by sum DESC,
where sum = (value amount where type = marks and status = up) - (value amount where type = marks and status = down)

为此，我使用 SQL：

select idn from Balans as outerB WHERE idn ! = '' group by idn order by 
ifnull((select sum(innerB.amount) from Balans as innerB 
    where innerB.idn = outerB.idn 
    and type='up'), 0) -
ifnull((select sum(innerB.amount) from Balans as innerB 
    where innerB.idn = outerB.idn 
    and type='down'), 0) DESC
limit 5

但在 SQL 中不正确ORDER by ... DESC

例如，在我的示例中，结果应该是：

187113012

6299927

测试 SQL 可以在这里找到

请告诉我如何编写正确的 SQL 选择？

Answer 1

怎么用CASE？

  SELECT idn,
         (SUM(CASE WHEN type = 'marks' AND status = 'up' THEN amount ELSE 0 END)-
         SUM(CASE WHEN type = 'marks' AND status = 'down' THEN amount ELSE 0 END)) 
         AS result
    FROM Balans b
   WHERE idn != ''
GROUP BY idn
ORDER BY result DESC
   LIMIT 5;

现场演示。

Answer 2

如果您愿意考虑更改数据库结构，我建议将金额存储为带符号的值，如果状态为“向上”则为正，如果状态为“向下”则为负。

在这些条件下，您的查询会简单得多。

SELECT idn, SUM(amount) as total
FROM Balans as outerB 
WHERE idn !='' AND type = 'marks'
GROUP BY idn 
ORDER BY total desc
LIMIT 5

但是，请注意，这不会返回表中没有任何“标记”的记录。如果您需要支持这一点，那么我认为您将重新使用CASE操作，类似于 Prix 答案中的查询。