Question

我正在尝试计算我的质心点的距离，这是通过标签的总数计算的，以及标签出现的即时时间的总和。这就是（tc_sum / cnt）的概念然而，子查询上的SELECT，不允许我得到质心点，因为“centr”尚未计算，因此我无法得到“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

Answer 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

Answer 2

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'

查询一行一行，您不能以这种方式引用别名。你必须再次“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。优化器将负责仅计算一次。但只有查询运行后才能知道别名。我担心我的英语太糟糕了，无法以一种好的方式解释它：）

MySQL获得子查询值

2 个答案: