Optimized count distinct for distributed VARCHAR columns
Details
| Detail name | Value |
|---|---|
| Changelog Number | 9258 |
| Type | Improvement |
| Status | Resolved |
| Fix Versions | Exasol 7.0.0 |
| Resolution Date | 2020-09-11 |
Background
Aggregations like
COUNT(DISTINCT <column>)
can be very expensive if there are a large number of distinct values in the column.
If the table is distributed on this column, there is an optimization that is applied, which can improve performance by a factor of 2-3. This count distinct optimization was only available for fixed columns so far.
Improvement
This optimization has been improved to support all relevant column data types.
