sum（当-condition-然后计数else 0结束的情况）
SELECT
SUM(case when $P{oneDayAgo} <= datetime then count else 0 end) as 'today',
SUM(case when $P{oneWeekAgo} <= datetime then count else 0 end) as 'thisweek',
SUM(count) as 'thismonth'
FROM
statistics
WHERE
name = "test"
AND $P{oneMonthAgo} <= datetime
AND datetime <= $P{Now}
请注意，如果需要平均值，请确保将NULL替换为0。
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