Question

我对SQL比较陌生，并希望学习一些简单的技巧。我设法创建了一个查询，选择每种不同类型的汽车许可证（ chargeType ），计算为每个许可证发出的数量（ num ），并添加一个列，显示签发的许可证总数（总计）。代码如下。

SELECT chargeType, 
       COUNT(chargeType) AS num,
       (SELECT COUNT(chargeType) 
       FROM permit) AS total
FROM permit
GROUP BY chargeType

我现在想要添加一个最终列，显示每个发布的许可类型的百分比。所以每种许可类型的数量除以总数乘以100，但我很难做到。有人可以帮忙吗？

Answer 1

尝试这样的事情

SELECT chargeType,
       num,
       total,
       num / NULLIF(total, 0) * 100 AS Percenatge
FROM   (SELECT chargeType,
               Count(chargeType) AS num,
               (SELECT Count(chargeType)
                FROM   permit)   AS total
        FROM   permit
        GROUP  BY chargeType) a

NULLIF用于避免除以零开始

Answer 2

这会奏效。此解决方案的优点是SELECT

中没有子查询

SELECT *, (num * 100 / total) as percentage
FROM 
(
SELECT
 chargeType, 
 COUNT(chargeType) AS num,
 total,
 (num * 100 / total) as percentage
FROM
  (SELECT COUNT(chargeType) as total FROM permit) ttotal
CROSS JOIN
  permit
GROUP BY
 chargeType
) tsub

SQL中的简单百分比列

2 个答案: