如何计算一段时间内的平均值？

Question

我试图在一段时间内获得平均值（例如：过去 6 个月、上个月、上周......）。

为此，我创建了 4 个查询。我可以清楚地做某事吗？

/** ON SELECTED DATE*/
SELECT AVG(RUN_TIME)
FROM (SELECT (DATEDIFF(minute,MIN(CAST(START_DATE AS DATETIME)), MAX(CAST(END_DATE AS DATETIME)))) as RUN_TIME FROM TableTest where DATE_EXPECTED = DATE_SELECTED ) f

/**ON 6 last month*/
SELECT AVG(RUN_TIME)
FROM (SELECT (DATEDIFF(minute,MIN(CAST(START_DATE AS DATETIME)), MAX(CAST(END_DATE AS DATETIME)))) as RUN_TIME  FROM TableTest 
where Month(CAST(DATE_SELECTED AS DATETIME)) BETWEEN Month(CAST(DATE_SELECTED AS DATETIME) ) AND Month(CAST(DATE_SELECTED AS DATETIME) )+6 ) f

/** on 30 last days */
SELECT AVG(RUN_TIME)
FROM (SELECT (DATEDIFF(minute,MIN(CAST(START_DATE AS DATETIME)), MAX(CAST(END_DATE AS DATETIME)))) as RUN_TIME  FROM TableTest where DATE_EXPECTED between DATE_SELECTED and DATE_SELECTED+30) f

/* on 5 last days */
SELECT AVG(RUN_TIME)
FROM (SELECT (DATEDIFF(minute,MIN(CAST(START_DATE AS DATETIME)), MAX(CAST(END_DATE AS DATETIME)))) as RUN_TIME  FROM TableTest where DATE_EXPECTED between DATE_SELECTED and DATE_SELECTED+5 ) f

它正在工作，但我想知道我是否能以最好的方式做这件事。

谢谢，

Answer 1

您可以使用条件聚合：

SELECT AVG(CASE WHEN DATE_EXPECTED = DATE_SELECTED THEN RUN_TIME END) as avg_1,
       AVG(CASE WHEN Month(CAST(DATE_SELECTED AS DATETIME)) BETWEEN Month(CAST(DATE_SELECTED AS DATETIME) ) AND Month(CAST(DATE_SELECTED AS DATETIME) )+6 THEN RUN_TIME END) as avg_2,
       AVG(CASE WHEN DATE_EXPECTED between DATE_SELECTED and DATE_SELECTED+30 THEN RUN_TIME END) as avg_3,
       AVG(CASE WHEN DATE_EXPECTED between DATE_SELECTED and DATE_SELECTED+5 THEN RUN_TIME END) as avg_4
FROM (SELECT (DATEDIFF(minute,MIN(CAST(START_DATE AS DATETIME)), MAX(CAST(END_DATE AS DATETIME)))) as RUN_TIME
      FROM TableTest
     ) f;