InfluxDB---Data exploration

1. The Group by clause and fill ()

In general, a group by interval uses a null output to represent data that has no value, and fill () can be used to change the output without a value. The Fill () option includes

• Any number
• NULL: Set NULL for output with no data within interval
• Previous: Copy the value of the previous interval as output without data
• None: Skip No value

The following example shows the use of fill ()

GROUP by without Fill ()

Example 1

SELECT MEAN(water_level) FROM h2o_feet WHERE time >= ‘2015-08-18‘ AND time < ‘2015-09-24‘ GROUP BY time(10d)
结果

name: h2o_feet--------------time                 mean2015-08-13T00:00:00Z   4.3062120833333232015-08-23T00:00:00Z   4.3189446293670292015-09-02T00:00:00Z   4.3638776812047812015-09-12T00:00:00Z   　4.69811470811633?2015-09-22T00:00:00Z

GROUP BY with fill()
例子2
Use fill() with -100:

SELECT MEAN(water_level) FROM h2o_feet WHERE time >= ‘2015-08-18‘ AND time < ‘2015-09-24‘ GROUP BY time(10d) fill(-100)

结果

name: h2o_feet--------------time                 mean2015-08-13T00:00:00Z   4.3062120833333232015-08-23T00:00:00Z   4.3189446293670292015-09-02T00:00:00Z   4.3638776812047812015-09-12T00:00:00Z   4.698114708116322?2015-09-22T00:00:00Z   -100

Example 3
Use fill() with none :

SELECT MEAN(water_level) FROM h2o_feet WHERE time >= ‘2015-08-18‘ AND time < ‘2015-09-24‘ GROUP BY time(10d) fill(none)
Results

name: h2o_feet--------------time               mean2015-08-13T00:00:00Z 4.3062120833333232015-08-23T00:00:00Z 4.3189446293670292015-09-02T00:00:00Z 4.3638776812047812015-09-12T00:00:00Z 4.69811470811633?

Note: If you use Group (ing) by something (for example, have tags and a time interval), fill () must be placed at the end of group by.

InfluxDB---Data exploration