Ole John Aske 1d6261c5c3 Fix for bug#58490, 'Incorrect result in multi level OUTER JOIN ...

in combination with IS NULL'
      
As this bug is a duplicate of bug#49322, it also includes test cases
covering this bugreport
      
Qualifying an OUTER JOIN with the condition 'WHERE <column> IS NULL',
where <column> is declared as 'NOT NULL' causes the
'not_exists_optimize' to be enabled by the optimizer.
      
In evaluate_join_record() the 'not_exists_optimize' caused
'NESTED_LOOP_NO_MORE_ROWS' to be returned immediately
when a matching row was found.
      
However, as the 'not_exists_optimize' is derived from
'JOIN_TAB::select_cond', the usual rules for condition guards
also applies for 'not_exist_optimize'. It is therefore incorrect
to check 'not_exists_optimize' without ensuring that all guards
protecting it is 'open'.
      
This fix uses the fact that 'not_exists_optimize' is derived from
a 'is_null' predicate term in 'tab->select_cond'. Furthermore,
'is_null' will evaluate to 'false' for any 'non-null' rows
once all guards protecting the is_null is open.
      
We can use this knowledge as an implicit guard check for the
'not_exists_optimize' by moving 'if (...not_exists_optimize)'
inside the handling of 'select_cond==false'. It will then
not take effect before its guards are open.
      
We also add an assert which requires that a
'not_exists_optimize' always comes together with
a select_cond. (containing 'is_null').

2011-02-01 15:19:34 +01:00

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