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what are the different query products in as400...?
Please explain what you mean by "in as 400"? Are you asking what query capabilities are available through the OS and the integrated DB2 for i? Or are you asking about query products that you can license?
The CPYF, RUNQRY, STRQMQRY, RUNSQLSTM and (in i 6.1 and later) RUNSQL commands are native. (RUNSQLSTM and RUNSQL aren't usually thought of as 'query' functions.) The SQL CLI APIs and the QQQQRY API are native. Other query capabilities are available through iSeries Navigator.
Essentially everything else is a product available through licensing.
and how do they function...
The documentation for native commands and APIs can be found in the Information Center that matches your OS release.
You will have to locate and ask each of the product developers to find out how the licensed products function. We have no way to know how they function.
Maybe the most commonly thought about is IBM's Query for i (Query/400) product. It's old, but sites continue to pay for it for some reason. IBM also provides Query Manager as part of SQL and the QM user interface as part of the SQL Development Kit licensed product; most sites have it and don't realize it.
After those, there are many 3rd-party query products. But that's just a research question that can be answered by Google searches. One Google result is Third-Party Competitors of Query for iSeries. That list is a few years old, but at least all of the major products on the list are still active. A few new ones can also be found by searching.