When using an OLAP data source, summaries that use 'For' clauses might give incorrect results due to the nature of OLAP data sources. Here’s why:

OLAP Data Structure:

Lack of Detail Rows: OLAP data sources are designed for multidimensional analysis and do not contain detail rows like relational databases. They store aggregated data at different levels of a hierarchy.

Implications for Summaries: Since the 'For' clause is used to generate summaries based on detail rows, applying it to an OLAP data source, which lacks these detail rows, can lead to incorrect or unexpected results.

Summarization Logic:

Aggregation Context: In OLAP, summarization is performed based on predefined hierarchies and aggregation rules, not on individual detail rows.

Correct Approach: When working with OLAP data, it’s essential to use functions and summarization techniques that are compatible with its structure.

Understanding the differences in data structures between OLAP and relational sources is critical for accurate report development.