Introduction to WQL: SQL for WMI - Schema Queries
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Schema Queries
Okay. We know how to build queries that return data information, and we know how to build queries that wait for new information. What if we want to know what type of information is available? Or more specifically, what type of information a specific class holds?
We can do this by checking the class’ schema. As you recall, the schema defines the type of information contained in the class. This third and final type of WMI query is the Schema Query. Take a look at this example.
SELECT * FROM meta_class WHERE __this ISA "Win32_BaseService"
This query returns all information for elements in the Win32_BaseService class. Building and using Schema queries is a bit beyond the scope of this article.
This is also, by far, the least used of all the query types. In fact, most scripters will probably never have a real-world use for it. A Google search should return some valuable results if you’re interested in learning more.
You may also want to check out the MSDN WQL Reference. It’s a very good resource explaining the different keywords available as well as the query structure.
I hope I’ve given you a workable introduction to the WMI Query Language. The only way to really learn WQL is to build a basic script and just start playing with it. It will come to you with practice.
Learning to become proficient in WMI will take your scripting to a whole new level. It’s much more powerful and comprehensive than WSH or VBS alone. Good luck in your scripting endeavors. Until next time…
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