From: Roy Lyseng
Date: February 8 2011 2:06pm
Subject: Re: bzr commit into mysql-trunk branch (jorgen.loland:3605) Bug#59793
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On 08.02.11 14.55, Øystein Grøvlen wrote:
> On 02/08/2011 01:08 PM, Roy Lyseng wrote:
>> Hi Jørgen,
>>
>> On 07.02.11 15.07, Jorgen Loland wrote:
>>> #At file:///export/home/jl208045/mysql/mysql-trunk-59793/ based on
>>> revid:tor.didriksen@stripped
>>>
>>> 3605 Jorgen Loland 2011-02-07
>>> Bug#59793: crash in Item_field::register_field_in_read_map
>>> with view
>>>
>>> Prior to the refactoring in this patch, Item_cond_xor behaved
>>> partially as an Item_cond and partially as an Item_func. The
>>> reasoning behind this was that XOR is currently not optimized
>>> (thus should be Item_func instead of Item_cond), but it was
>>> planned optimize it in the future (thus, made Item_cond anyway
>>> to ease optimization later).
>>
>> I dislike this solution, because conceptually an XOR is an Item_cond,
>> regardless of whether it is being optimized or not, and regardless of
>> whether an optimization is planned for it.
>
> IIUC, in the MySQL code an Item_cond represents a Boolean function with an
> unlimited number of arguments, while Item_bool_func2 is a Boolean function with
> two arguments. The current implementation of XOR can only operate on two
> arguments. Hence it is not really an Item_cond.

I consider it an "Item_cond" because it is on the same level as AND and OR in 
the syntax diagrams. Whether it takes two or more arguments is strictly not 
relevant.

The reason that Item_cond for AND and OR can take more than two arguments is the 
optimization of such functions, and not based on syntax.

Roy