WQL does not support TOP - need workaround

Question

WQL (basically SQL for WMI) does not support a TOP or LIMIT keyword. Sql Server used TOP and many other RDBMSs supprt LIMIT etc.

Is there a workaround to emulating a SELECT query to behave as though it had a TOP/LIMIT clause that limits the result set to some arbitrary number?

Or is there some other WQL-specific keyword that works like TOP or LIMIT?

Answer 1

Nope, there's no way to simulate TOP using WQL alone.

Exception: if you're lucky enough to be querying a WMI class which has ungapped, ascending numeric instance numbers used as keys, then you can use greater-than and less-then comparisons to limit and page through the results.

It's possible that ManagementClass.GetInstances() instead of using a WQL query might allow you to cancel the enumeration midway once you've collected enough instances, and hence avoid paying the CPU and RAM cost of enumerating the whole list at once.

Note that, AFAIK, the CIMV2 WMI provider doesn't natively handle WQL-- instead it simply relies on WMI to enumerate all instances, process the WQL, and filter the results before returning them to the caller. But the expensive part (actually fetching the underlying WMI data) is still done. So I believe there's no efficiency gain to be had (for local WMI queries, that is) by using WQL vs. using GetInstances() and filtering the results yourself-- and if GetInstances() allows you to cancel midway, then GetInstances() may be much cheaper for long result sets.