我有以下询问:
SELECT AVG(val) from floatTable
WHERE tagindex IN(1,2,3,4)
AND DateAndTime > $first_of_year
这一年,这四面的数值平均值保持不变。 自2006年以来 我已经恢复这一数据,我如何能够从本月第一个月,即一周第一周以来和午夜之后获得数据? 我已经把这些日期计算为每月第一美元、每周第一美元和午夜美元。 我试图尽量减少问询,希望有人会帮助我 whi开一些魔.,在单一问询或最优化的问询中恢复这一数据。 平均需要300秒钟,因此,我希望尽可能少地这样做。
事先感谢你。
SELECT AVG(case when DateAndTime > $first_of_year then val end) as FirstOfYear,
AVG(case when DateAndTime > $first_of_month then val end) as FirstOfMonth,
AVG(case when DateAndTime > $first_of_week then val end) as FirstOfWeek,
AVG(case when DateAndTime > $midnight then val end) as Midnight
from floatTable
WHERE tagindex IN(1,2,3,4)
and DateAndTime > $first_of_year
为了改进业绩,确保您在<代码>DateAndtime和栏目<>上有索引。
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