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From:Baron Schwartz Date:August 29 2007 5:39pm
Subject:Re: what does "index map: N" mean?
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Hi,

Sergey Petrunia wrote:
> Hi!
> 
> On 8/29/07, Baron Schwartz <baron@stripped> wrote:
>> Sometimes in EXPLAIN output, I see this in the Extra field:
> ...
>> explain select * from t1, t1 t2 where t1.y = 2 and t2.x between 7 and
>> t1.y+0;
>> id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
>> 1	SIMPLE	t1	ref	y	y	5	const	1	Using where
>> 1	SIMPLE	t2	range	x	x	5	NULL	4	Range checked for each record (index map: 0x1)
>>
>> I know what the rest of it means, but what does 0x1 mean?
> 
> It is a bitmap of indexes which can be used by range/index_merge
> access that is performed for each row combination of the preceding
> tables.

Thanks Sergey, Chad.  Follow-up question: can I assume that in the 
output of SHOW CREATE TABLE, 0x1 is the first index, 0x2 is the second, 
0x3 is the first and second -- in the order they appear in that output? 
  If not, how would I be able to tell which indexes the bitmap refers to?

Thanks
Baron
Thread
what does "index map: N" mean?Baron Schwartz29 Aug
  • Re: what does "index map: N" mean?Chad MILLER29 Aug
  • Re: what does "index map: N" mean?Sergey Petrunia29 Aug
    • Re: what does "index map: N" mean?Baron Schwartz29 Aug
      • Re: what does "index map: N" mean?Jay Pipes29 Aug
        • Re: what does "index map: N" mean?Baron Schwartz30 Aug
          • Re: what does "index map: N" mean?Hartmut Holzgraefe30 Aug
            • Re: what does "index map: N" mean?Paul DuBois30 Aug
Re: what does "index map: N" mean?Hartmut Holzgraefe3 Sep
  • Re: what does "index map: N" mean?Baron Schwartz3 Sep
    • Re: what does "index map: N" mean?Baron Schwartz5 Sep