Interpolated retrieval - query 3

SELECT TagName, DateTime, Value, QualityDetail, wwInterpolationType

FROM History

WHERE TagName = 'A001'

AND DateTime >= '2009-09-12 00:20'

AND DateTime <= '2009-09-12 00:40'

AND wwRetrievalMode = 'Interpolated'

AND wwResolution = '10000'

This query can be run against the following sample data:

The following is a graphical representation of the data:

The results are:

The sample data points and the results are mapped on the following chart. Only the data falling between the time start and end marks at 00:20 and 00:40 (shown on the chart as dark vertical lines) are returned by the query.

Because there is no value that matches the start time, an initial value at 00:20 is returned in the results based on the preceding data point at 00:17 because the following data point at 00:22 is NULL. Because a NULL value precedes the 00:30 cycle boundary at 00:29, the NULL is returned at the cycle boundary. The value at 00:40 is an interpolation of the data points at 00:38 and 00:42.