Tableau‘s LOD expressions are extremely powerful. They allow users to control how Tableau aggregates data. This is particularly important when we join tables with different level of aggregation. For example, combining transaction level data with store level data means that we may want to SUM across transaction variables but only AVG over store variables. More examples are here. Unfortunately, learning LOD expressions is not straightforward. I┬ácame up with this absolute minimal example that illustrates the behavior of Tableau’s LOD expressions.