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Bug#46454: MySQL wrong index optimisation leads to incorrect result & crashes

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Problem 1:
When the 'Using index' optimization is used, the optimizer may still - after
cost-based optimization - decide to use another index in order to avoid using
a temporary table. But when this happens, the flag to the storage engine to 
read index only (not table) was still set. Fixed by resetting the flag in the 
storage engine and TABLE structure in the above scenario, unless the new index
allows for the same optimization.
Problem 2:
When a 'ref' access method was employed by cost-based optimizer, (when the column
is non-NULLable), it was assumed that it needed no initialization if 'quick' access
methods (since they are based on range scan). When ORDER BY optimization overrides 
the decision, however, it expects to have this initialized and hence crashes. 
Fixed in 5.1 (was fixed in 6.0 already) by initializing 'quick' even when there's 
'ref' access. 

mysql-test/r/order_by.result:
  Bug#46454: Test result.
mysql-test/t/order_by.test:
  Bug#46454: Test case.
sql/sql_select.cc:
  Bug#46454: 
  Problem 1 fixed in make_join_select()
  Problem 2 fixed in test_if_skip_sort_order()
sql/table.h:
  Bug#46454: Added comment to field.
This commit is contained in:
Martin Hansson
2009-08-07 13:51:40 +02:00
parent 439e1eb0e0
commit 4c3917b6f8
4 changed files with 118 additions and 13 deletions
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8
sql/table.h
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@ -755,7 +755,13 @@ struct st_table {
*/
my_bool force_index;
my_bool distinct,const_table,no_rows;
my_bool key_read, no_keyread;
/**
If set, the optimizer has found that row retrieval should access index
tree only.
*/
my_bool key_read;
my_bool no_keyread;
/*
Placeholder for an open table which prevents other connections
from taking name-locks on this table. Typically used with