I've been testing 3rd-party query-building solutions for OLAP data warehouses with a few of our product's mostly non-technical business users, and I've had trouble finding any that are simple enough for our users. To give you an idea of the challenge, most of our users have never built a Pivot Table in Excel.
Our users' reporting use-cases are simple, e.g. basic tabular reports, e.g. "Sales and Returns by Salesperson in 2014" or "Sales, Purchases, and Inventory, by product, in the last month".
For our users and these use cases, OLAP query builders I've tested seem like overkill. Here's one example below for finding and choosing columns to add to a query:

Our users report a few problems here:
- "I don't like having to dig into a tree to find anything. Everything is hidden. I know the name of a column I want, but I don't know where to find it."
- "I don't understand what 'measures' means. I just want columns to add to my report."
- "Why is 'Sales Orders' under Measures but 'Product' is not?
- "When I drag columns over to my report, it creates a multi-level table [example below]. I just want a regular table without any levels."

Translating these users' concerns into tech-speak, these users were baffled by basic BI concepts:
- the difference between facts (measures) and dimensions
- dimension hierarchies
- the concept of a "database table", especially the idea that there are some limitations in how data from different tables can be combined/joined.
- pivot tables (in general) and specifically the interaction between pivoting and aggregation
- how to get a simple tabular view from a more complex pivot-table view
We could abandon the project and simply build a lot of canned reports instead. But we know from user interviews that the ability to add and remove columns from reports is at the top of our users' priority lists-- and is an important differentiator from our competitors who have limited reporting flexibility.
I'm sure I'm not the first person to discover that even simple OLAP query builders aren't simple enough for some users, so was hoping that the UX experts here might be able to point me in the right direction.
Are there well-known really-simple UX patterns for making tabular reports from OLAP and/or Dimensionally-Modelled relational sources? Is there good user research about conceptually simpler ways to build OLAP queries?
I've done lots of Googling and reading dry usability research reports without much luck so far.
