> ------------------------------------------------------------
> revno: 3181
> revision-id: alexey.kopytov@sun.com-20091016201951-fsht0wm8xn8vkzsx
> parent: joerg@mysql.com-20091016164025-kb4sbrggq5o7zufc
> committer: Alexey Kopytov <Alexey.Kopytov@Sun.com>
> branch nick: mysql-5.1-bugteam
> timestamp: Sat 2009-10-17 00:19:51 +0400
> message:
>   Bug #47123: Endless 100% CPU loop with STRAIGHT_JOIN 
>    
>   The problem was in incorrect handling of predicates involving 
>   NULL as a constant value by the range optimizer. 
>    
>   For example, when creating a SEL_ARG node from a condition of 
>   the form "field < const" (which would normally result in the 
>   "NULL < field < const" SEL_ARG),  the special case when "const" 
>   is NULL was not taken into account, so "NULL < field < NULL" 
>   was produced for the "field < NULL" condition. 
>    
>   As a result, SEL_ARG structures of this form could not be 
>   further optimized which in turn could lead to incorrectly 
>   constructed SEL_ARG trees. In particular, code assuming SEL_ARG 
>   structures to always form a sequence of ordered disjoint 
>   intervals could enter an infinite loop under some 
>   circumstances. 
>    
>   Fixed by changing get_mm_leaf() so that for any sargable 
>   predicate except "<=>" involving NULL as a constant, "empty" 
>   SEL_ARG is returned, since such a predicate is always false.