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我正在尝试计算质心点的距离，这是通过标签总数和标签出现的瞬间时间总和计算得出的。这就是 (tc_sum/cnt) 的概念。
但是，子查询上的 SELECT 不允许我获得质心点，因为尚未计算“中心”，所以我无法获得“距离”。
有什么帮助吗？

SELECT cnt, tc_sum, ROUND(tc_sum/cnt) as centr, distance
FROM (
    SELECT SUM(timecode) as tc_sum, count(timecode) as cnt, ABS( centr - '".$timecode."' ) AS distance
    FROM dados d
    WHERE tag = 'donald'
    AND filename = 'donald.mp4'
    AND group_id = '1'
    ) d
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2 回答 2

1

尝试

SELECT cnt, tc_sum, ROUND(tc_sum/cnt) as centr, distance
FROM (
SELECT SUM(timecode) as tc_sum, count(timecode) as cnt, ABS( ROUND(tc_sum/cnt)- '".$timecode."' ) AS  distance
FROM dados d
WHERE tag = 'donald'
AND filename = 'donald.mp4'
AND group_id = '1'
) d
于 2013-02-28T11:36:10.673 回答
1 
SELECT 
 SUM(timecode) as tc_sum, 
 SUM(timecode) as cnt, 
 ABS( SUM(timecode) / SUM(timecode) - '".$timecode."' ) AS distance, 
 ROUND(SUM(timecode) / SUM(timecode)) AS centr
FROM dados d
WHERE tag = 'donald'
 AND filename = 'donald.mp4'
 AND group_id = '1'

查询逐行运行，您不能以这种方式引用别名。您必须再次“重新计算”它们。“重新计算”不是正确的词，因为结果并没有真正计算多次。优化器会处理它只计算一次。但是只有在查询运行后才知道别名。恐怕我的英语太烂了，无法很好地解释它:)

于 2013-02-28T11:38:27.260 回答