Question

我不确切地知道如何说出这个问题但在这里。我想重用我在查询中计算的值来计算另一个值。变量是我猜的正确的单词。这是我的疑问：

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 ...

内部回合我想使用SUM返回的值（t1.totalEvents），但当我使用Entry时，我收到此错误Unknown column 'Entry' in 'field list'

如果没有像这样重新计算，我怎么能在那里获得价值：

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

Answer 1

看一下这个例子

select (select @t1:=sum(field1)),(select @t2:=sum(field2)),@t1/@t2 from table

Answer 2

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;

Answer 3

一种选择是在FROM子句中使用子查询，如：

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

如果你想在进一步的查询中重用Rate，那么它会变得复杂，我不知道这是否会有最佳性能，但我认为它会做你在你的例子中所要求的。

Mysql - 重用计算值

3 个答案: