Re: what does "index map: N" mean?

On 29 Aug 2007, at 12:26, Baron Schwartz wrote:
> 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?

Hi Baron. I've never seen this code before, but (grain of salt!) from my first look it looks like it's a bitmap of which columns are treated as keys for searching. So, possible values would have been 0x1, 0x2, and (maybe) 0x3. I admit it's not good phrasing. It would be better to say "index on columns (x)", if we even have the column name any more at that point.

So, that's my guess. There's some voodoo in there that I don't yet understand and I may be completely wrong.

• chad

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Chad Miller, Software Developer                         chad@mysql.com
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