DuplicateWeedout strategy
You are viewing an old version of this article. View
the current version here.
DuplicateWeedout is an execution strategy for Semi-join subqueries.
The idea
The idea is to run semi-join as if it was a regular join, and then eliminate the duplicate record combinations using a temporary table.
DuplicateWeedout in action
TODO
Factsheet
- DuplicateWeedout is shown as "Start temporary/End temporary" in EXPLAIN
- The strategy can handle correlated subqueries, but cannot be applied if the subquery has grouping or aggregate functions.
- DuplicateWeedout allows the optimizer to freely mix subquery's tables and parent select's tables.
Comments
Comments loading...
Content reproduced on this site is the property of its respective owners,
and this content is not reviewed in advance by MariaDB. The views, information and opinions
expressed by this content do not necessarily represent those of MariaDB or any other party.
