Question

我有一个以EID作为主键的表（它是一个varchar并包含一些细节）和uploadtime作为日期时间列。我希望这张表的结果为：

substr(eid,5,5) as machine | count(eid) in group(grouped by machine) as packets | AvgDelay (as shown in SQL code) | packets * AvgDelay as Penalty

但是最后一列始终为null。我使用的SQL是：

SELECT substr(eid, 5, 5) AS machine,
@packetcount: = count(*) AS packets,
@avg_delay: = round(avg(DATEDIFF(IF (STR_TO_DATE(uploadtime, '%Y-%m-%d') IS NULL, CURDATE(), STR_TO_DATE(uploadtime, '%Y-%m-%d')), STR_TO_DATE(SUBSTR(eid, 15, 8), '%Y%m%d') ) ) ) AS AvgDelay, 
@packetcount * @avg_delay AS Penalty 
FROM eidreport
WHERE uploadtime IS NOT NULL
OR DATEDIFF(IF (STR_TO_DATE(uploadtime, '%Y-%m-%d') IS NULL, CURDATE(), STR_TO_DATE(uploadtime, '%Y-%m-%d')), STR_TO_DATE(SUBSTR(eid, 15, 8), '%Y%m%d') ) >= 100 
GROUP BY machine

Here is the link for SQL Fiddle

我哪里错了？请帮忙。提前谢谢。

Answer 1

我认为这里的问题在GROUP BY声明中。我认为@packetcount: = count(*)在分组之后计算但@packetcount * @avg_delay之前计算，所以在这一刻它们是未定义的。

尝试使用这样的子查询：

SELECT *,
packets * AvgDelay AS Penalty

FROM
(
select substr(eid,5,5) as machine,count(*) as packets,
round(avg(DATEDIFF(IF(STR_TO_DATE(uploadtime, '%Y-%m-%d') IS NULL, CURDATE(), STR_TO_DATE(uploadtime, '%Y-%m-%d')),
                      STR_TO_DATE(SUBSTR(eid, 15, 8),'%Y%m%d')))) AS AvgDelay
from eidreport
where uploadtime is not null or
DATEDIFF(
  IF(STR_TO_DATE(uploadtime, '%Y-%m-%d') IS NULL, CURDATE(), STR_TO_DATE(uploadtime, '%Y-%m-%d')),
  STR_TO_DATE(SUBSTR(eid, 15, 8),'%Y%m%d')) >= 100
group by machine
) as T

SQLFiddle example

Answer 2

为什么在不需要时使用子查询：

SELECT
    SUBSTR(eid,5,5) machine,
    COUNT(1) packets,
    ROUND(AVG(DATEDIFF(IF (STR_TO_DATE(uploadtime, '%Y-%m-%d') IS NULL,
                        CURDATE(), STR_TO_DATE(uploadtime, '%Y-%m-%d')),
                        STR_TO_DATE(SUBSTR(eid, 15, 8), '%Y%m%d') ) ) ) AvgDelay,
    COUNT(1) * ROUND(AVG(DATEDIFF(IF (STR_TO_DATE(uploadtime, '%Y-%m-%d') IS NULL,
                        CURDATE(), STR_TO_DATE(uploadtime, '%Y-%m-%d')),
                        STR_TO_DATE(SUBSTR(eid, 15, 8), '%Y%m%d') ) ) ) Penalty
FROM
    eidreport
WHERE uploadtime IS NOT NULL
OR DATEDIFF(IF (STR_TO_DATE(uploadtime, '%Y-%m-%d') IS NULL, CURDATE(),
            STR_TO_DATE(uploadtime, '%Y-%m-%d')),
            STR_TO_DATE(SUBSTR(eid, 15, 8), '%Y%m%d') ) >= 100 
GROUP BY machine

optimers仅评估相同的表达式

在select子句中分配和使用mysql用户变量

2 个答案: