結合SQL選擇查詢

Question

我有2個不同的查詢，它們都返回類似於下面的結果。 例如

SELECT value
     , date_format( statdate, "%Y-%m-%d" ) AS testdate
FROM stats
WHERE name LIKE 'myname1'
    AND date >= "2014-09-20"
    and date < "2014-09-24"
GROUP BY 2;

SELECT value
    , date_format( statdate, "%Y-%m-%d" ) AS testdate
FROM stats
WHERE name LIKE 'myname2'
    AND date >= "2014-09-20"
    and date < "2014-09-24"
GROUP BY 2;

信息來自同一張表，但部分信息來自不同的WHERE（日期是字段，兩者均相同）。

兩者都返回類似的信息。

value| testdate  |
+--------+-------+
| 60 | 2014-09-20|
| 57 | 2014-09-21|
| 56 | 2014-09-22|
| 55 | 2014-09-23|
| 59 | 2014-09-24|

我想做的是將兩組結果組合為一個（然后對兩個數字進行比率等數學運算），所以我想得到類似...

val1 | val2| ratio (val1/val2) | testdate   |
+----+-------------------------|------------+
| 60 | 140 | 0.42              | 2014-09-20 |
| 57 | 180 | 0.31              | 2014-09-21 |
| 56 | 190 | 0.29              | 2014-09-22 | 
| 55 | 10  | 5.5               | 2014-09-23 |
| 59 | 100 | 0.59              | 2014-09-24 |

我猜我需要在某個地方JOIN一個JOIN ，但無法弄清楚，以及如何在其中使用此值進行一些基本數學JOIN ？

Answer 1

您應該使用“ Self Join ”來聯接同一表的2個實例。 像下面

SELECT s1.value, date_format( s1.statdate, "%Y-%m-%d" ) AS testdate
s2.value, date_format( s2.statdate, "%Y-%m-%d" ) AS testdate2,
(s1.value/s2.value) as ration
FROM stats s1, stats s2
WHERE s1.id = s2.id 
and s1.name LIKE 'myname1' AND s1.date >= "2014-09-20" and s1.date < "2014-09-24" 
and s2.name LIKE 'myname2' AND s2.date >= "2014-09-20" and s2.date < "2014-09-24" 
GROUP BY 2;

Answer 2

我建議條件聚合：

SELECT date_format(statdate, '%Y-%m-%d') AS testdate,
       max(case when name = 'myname1' then value end) as val1,
       max(case when name = 'myname2' then value end) as val2,
       (max(case when name = 'myname1' then value end) /
        max(case when name = 'myname2' then value end)
       ) as ratio,
FROM stats
WHERE name in ('myname1', 'myname2') AND date >= '2014-09-20' and date < '2014-09-24'
GROUP BY date_format(statdate, '%Y-%m-%d');