Merging InfoTables can seem to be an overwhelming task in ThingWorx. What even IS an InfoTable?? The short answer is that an InfoTable is a specifically structured JSON object. Merging InfoTables is therefore as easy as incrementing through each, adding the columns of each to another table, and then populating the new table with data.
For InfoTables with the same DataShapes, the built in "Union" service can be used. Find this snippet under the InfoTableResources section. There is also a snippet for incrementing through DataShape fields if the DataShape is known. For InfoTables which don't have the same DataShapes or for which the DataShape is not known, things get a bit trickier. Thankfully, some new KCS documentation provides example code to step you through merging any number of tables together.