History version - query example

This example illustrates using history version. First, consider this query:

SELECT TagName, DateTime, Value, wwVersion

FROM History

WHERE TagName IN ('SysTimeHour', 'SysTimeMin')

AND DateTime >= '2001-12-20 0:00'

AND DateTime <= '2001-12-20 0:05'

AND wwRetrievalMode = 'Delta'

AND wwVersion = 'Original'

The results are:

When retrieving the latest version, the wwVersion parameter always returns with a value of LATEST for all values, even though many of the values may actually be the original values that came from the I/O Server. To distinguish between an actual latest value and an original value, a special QualityDetail of 202 is returned for a good, latest point. Note, however, that replicated data may show a QualityDetail of 202 for points other than the latest point.

For example:

SELECT DateTime, Value, Quality, QualityDetail, OPCQuality, wwVersion

FROM History

WHERE TagName IN ('PV')

AND DateTime >= '2005-04-17 11:35:00'

AND DateTime <= '2005-04-17 11:36:00'

AND wwRetrievalMode = 'Delta'

AND wwVersion = 'Latest'

The results are: