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authorunknown <knielsen@knielsen-hq.org>2012-08-24 13:57:39 +0200
committerunknown <knielsen@knielsen-hq.org>2012-08-24 13:57:39 +0200
commitcaa535eb9fa97bd7c2190292bb4a3a3c1aaa71e3 (patch)
tree443fee6698968975faaeadba6ca0d5a532667b18 /sql/opt_subselect.cc
parent6c3a756dd92af851f421bd9791d4b6b95063b484 (diff)
parente44a800d91a887119d3b612276b37f09b076fee1 (diff)
downloadmariadb-git-caa535eb9fa97bd7c2190292bb4a3a3c1aaa71e3.tar.gz
Merge from 5.3
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3.2.1 Non-merged semi-joins and join optimization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For join optimization purposes, non-merged semi-join nests are similar to
- base tables - they've got one JOIN_TAB, which can be accessed with one of
- two methods:
+ base tables. Each such nest is represented by one one JOIN_TAB, which has
+ two possible access strategies:
- full table scan (representing SJ-Materialization-Scan strategy)
- eq_ref-like table lookup (representing SJ-Materialization-Lookup)
Unlike regular base tables, non-merged semi-joins have:
- non-zero JOIN_TAB::startup_cost, and
- join_tab->table->is_filled_at_execution()==TRUE, which means one
- cannot do const table detection or range analysis or other table data-
- dependent inferences
- // instead, get_delayed_table_estimates() runs optimization on the nest so that
- // we get an idea about temptable size
+ cannot do const table detection, range analysis or other dataset-dependent
+ optimizations.
+ Instead, get_delayed_table_estimates() will run optimization for the
+ subquery and produce an E(materialized table size).
3.2.2 Merged semi-joins and join optimization
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~