[Maria-developers] How to get all fields in a given index?
Hi, 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? Thanks! Rongrong
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
Thanks a lot! Rongrong Rongrong On Tue, Sep 9, 2014 at 8:18 AM, Sergey Petrunia <sergey@mariadb.com> wrote:
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
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