Sql 如何计算一段时间内的平均值？

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。我能清楚地做点什么吗

/** 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

这是有效的，但我想知道我是否能以最好的方式做这件事

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谢谢，

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;

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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;

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是的，我想要一个平均值。我仍然在学习：我不应该使用平均值？你应该看看这篇关于使用日期快捷方式的文章。是的，我想要一个平均值。我仍然在学习：我不应该使用平均值？你应该看看这篇关于使用日期快捷方式的文章。我的不同查询的结果不同。我对所有的平均值都有相同的结果（而且不应该）@FannyV。对于这四个

avg（）

调用，数据必须非常特殊，才能返回相同的值。我对所有的平均值都有相同的结果（而且不应该）@FannyV。对于这四个

avg（）

调用，要返回相同的值，数据必须非常特殊。