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Data & Analytics · Advanced

Chasm Trap

An error that occurs when two fact tables are joined through a shared dimension, multiplying rows and overstating measures from both.

Definition

Querying sales and returns joined through Customer in one SQL statement creates a many-to-one-to-many path. The fix is to aggregate each fact separately, then combine the results (drill-across).

Exam tip

Combine multiple facts by aggregating separately and then joining on conformed dimensions.

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