Low Performance for nested simple CASE expression in GROUP BY
Details
| Detail name | Value |
|---|---|
| Changelog Number | 11408 |
| Type | Bug |
| Status | Resolved |
| Affected Versions | Exasol 6.2.0, Exasol 7.0.0 |
| Fix Versions | Exasol 7.0.7, Exasol 6.2.14 |
| Resolution Date | 2021-02-02 |
Description
Statements using a nested simple CASE expression in GROUP BY have a high runtime.
Example:
SELECT
CASE (CASE ... WHEN ... END) WHEN ... END,
SUM(...)
FROM t
GROUP BY 1;
Workaround
- Either replace the nested CASE expressions with nested DECODE expressions,
- or replace the nested CASE expressions with a single non-nested CASE expression.
Fix
The fix will reduce the runtime of affected statements.
