On Mon, Sep 08, 2014 at 08:54:00PM +0100, Rongrong wrote:
> I'm trying to implement some feature that requires to get the list of
> fields for a given index. I'm trying to follow the optimizer code to find
> some clue but am not successful so far. Can anyone give me some pointers?
>

A TABLE object has a member called key_info. It is an array of structures
describing each index.

For an index $I, table->key_info[$I].usable_key_parts gives the number of key
parts that the optimizer considers (it varies depending on extended_keys=on|off
setting),

Then, table->key_info[$I].key_part is an array of structures describing key
parts.
The most interesting are table->key_info[$I].key_part[$PART].field (the field
itself) and table->key_info[$I].key_part[$PART].fieldnr (field number).


Alternatively, there is table->field[$FIELD_NO].part_of_key - this is a bitmap
which tells which indexes this field is a part of.

BR
 Sergei
--
Sergei Petrunia, Software Developer
MariaDB | Skype: sergefp | Blog: http://s.petrunia.net/blog