MySQL-重用计算值 [英] Mysql - reusing calculated values

问题描述

我不知道该怎么表达这个问题，但确实如此. 我想重用我在查询中计算出的值来计算另一个值. 变量是我猜的正确词.这是我的查询:

I don't know exactly how to word this question but here it is. I want to reuse values that i calculated in my query to calculate another value. Variables is the correct word i guess. here is my query:

SELECT 
    t1.label as label,SUM(t1.totalEvents) as Entry,SUM(t2.totalEvents) as Back,  
    ROUND(Entry/Back*100,2) as 'Rate'
FROM 
    trackReports_daily t1
.... rest of query ...

在内部回合中，我想使用SUM(t1.totalEvents)返回的值，但是当我使用Entry时，出现此错误Unknown column 'Entry' in 'field list'

Inside round i want to to use the value returned by SUM(t1.totalEvents), but when i use Entry i get this error Unknown column 'Entry' in 'field list'

我又如何在不重新计算的情况下获得其中的值:

How else can i get the value in there without recalculating everytime like this:

ROUND(SUM(t2.totalEvents)/SUM(t1.totalEvents)*100,2)

推荐答案

您可以使用子查询:

SELECT label, Entry, Back, ROUND(Entry/Back*100,2) as 'Rate'
FROM (
    SELECT SUM(t1.totalEvents) as Entry, SUM(t2.totalEvents) as Back, t1.label as label
    FROM trackReports_daily t1 
    .... rest of query ... 
) as temp;

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