# `HashAgg` Process

![`smart`](HASHAGG01_aa_003_20231013.png)

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Next, let's explain the principle of the `HashAgg` operator.

In the diagram, we have the salary table for each employee, and we want to compute aggregation results, such as sum, average, or count, grouped by the `department` column. The process begins by sequentially reading each row from the table. As rows are processed, they are aggregated by `department`, summing and counting the values accordingly.