Improved performance for queries containing CHAR/VARCHAR joins
Details
| Detail name | Value |
|---|---|
| Changelog Number | 124 |
| Type | Improvement |
| Status | Resolved |
| Fix Versions | Exasol 7.1.1 |
| Resolution Date | 2021-09-14 |
Background
Expression indexes are temporary indexes that are built when a join condition is on an expression instead of a table column. This can happen when joining on columns of different data types, for example. Since index creation is a comparatively expensive operation, it is more beneficial to (re-)use a table index instead of an expression index.
Joining between string types (VARCHAR and CHAR) may use an expression index even though the join is only on the columns.
Improvement
A table index is used instead of an expression index for all equi joins on columns of types VARCHAR and CHAR. This results in better performance for columns containing these joins because an expression index does not have to be re-built during query execution.
