ROM "h2o_feet" WHERE time >= '2015-08-18T00:00:00Z' AND time <= '2015-08-18T00:30:00Z' group by time(12m), *
name: h2o_feet
tags: location=coyote_creek
time derivative
---- ----------
2015-08-18T00:12:00Z -0.11900000000000022
2015-08-18T00:24:00Z -0.12849999999999984name: h2o_feet
tags: location=santa_monica
time derivative
---- ----------
2015-08-18T00:12:00Z -0.00649999999999995
2015-08-18T00:24:00Z -0.015499999999999847
这个计算其实是先根据GROUP BY time求平均值，然后对这个平均值再做变化比的计算。因为数据是按12分钟分组的，而变化比的unit是6分钟，所以差值除以2(12/6)才得到变化比。如第一个值是 (7.8245-8.0625)/2 = -0.1190。
> SELECT mean("water_level") FROM "h2o_feet" WHERE time >= '2015-08-18T00:00:00Z' AND time <= '2015-08-18T00:30:00Z' group by time(12m), *
name: h2o_feet
tags: location=coyote_creek
time mean
---- ----
2015-08-18T00:00:00Z 8.0625
2015-08-18T00:12:00Z 7.8245
2015-08-18T00:24:00Z 7.5675name: h2o_feet
tags: location=santa_monica
time mean
---- ----
2015-08-18T00:00:00Z 2.09
2015-08-18T00:12:00Z 2.077
2015-08-18T00:24:00Z 2.0460000000000003
NON_NEGATIVE_DERIVATIVE与DERIVATIVE不同的是它只返回的是非负的变化比:
> SELECT DERIVATIVE(mean("water_level"), 6m) FROM "h2o_feet" WHERE location='santa_monica' AND time >= '2015-08-18T00:00:00Z' AND time <= '2015-08-18T00:30:00Z' group by time(6m), *
name: h2o_feet
tags: location=santa_monica
time derivative
---- ----------
2015-08-18T00:06:00Z 0.052000000000000046
2015-08-18T00:12:00Z -0.08800000000000008
2015-08-18T00:18:00Z 0.09799999999999986
2015-08-18T00:24:00Z -0.08499999999999996
2015-08-18T00:30:00Z 0.010000000000000231
> SELECT NON_NEGATIVE_DERIVATIVE(mean("water_level"), 6m) FROM "h2o_feet" WHERE location='santa_monica' AND time >= '2015-08-18T00:00:00Z' AND time <= '2015-08-18T00:30:00Z' group by time(6m), *
name: h2o_feet
tags: location=santa_monica
time non_negative_derivative
---- -----------------------
2015-08-18T00:06:00Z 0.052000000000000046
2015-08-18T00:18:00Z 0.09799999999999986
2015-08-18T00:30:00Z 0.010000000000000231
4 连续查询
4.1 基本语法
连续查询(CONTINUOUS QUERY，简写为CQ)是指定时自动在实时数据上进行的InfluxQL查询，查询结果可以存储到指定的measurement中。基本语法格式如下：
CREATE CONTINUOUS QUERY <cq_name> ON <database_name>
BEGIN
<cq_query>
END
cq_query格式： SELECT <function[s]> INTO <destination_measurement> FROM <measurement> [WHERE <stuff>] GROUP BY time(<interval>)[,<tag_key[s]>]
CQ操作的是实时数据，它使用本地服务器的时间戳、GROUP BY time()时间间隔以及InfluxDB预先设置好的时间范围来确定什么时候开始查询以及查询覆盖的时间范围。注意CQ语句里面的WHERE条件是没有时间范围的，因为CQ会根据GROUP BY time()自动确定时间范围。
CQ执行的时间间隔和GROUP BY time()的时间间隔一样，它在InfluxDB预先设置的时间范围的起始时刻执行。如果GROUP BY time(1h)，则单次查询的时间范围为 now()-GROUP BY time(1h)到 now()，也就是说，如果当前时间为17点，这次查询的时间范围为 16:00到16:59.99999。
下面看几个示例，示例数据如下，这是数据库transportation中名为bus_data的measurement，每15分钟统计一次乘客数和投诉数。数据文件bus_data.txt如下：
# DDLCREATE DATABASE transportation
# DML
# CONTEXT-DATABASE: transportation bus_data,complaints=9 passengers=5 1472367600
bus_data,complaints=9 passengers=8 1472368500
bus_data,complaints=9 passengers=8 1472369400
bus_data,complaints=9 passengers=7 1472370