Question

I’ve checked numerous other SO posts and MySQL docs but can’t seem to get an answer on why an index isn’t being used, and how to force it to be used – I can see many others are having similar problems, but can’t find a solution.

The table looks like this

CREATE TABLE `countries_ip` (
`ipfrom` INT(10) UNSIGNED ZEROFILL NOT NULL,
`ipto` INT(10) UNSIGNED ZEROFILL NOT NULL,
`countrySHORT` CHAR(2) NULL DEFAULT NULL,
`country_id` INT(10) UNSIGNED NOT NULL,
PRIMARY KEY (`ipfrom`, `ipto`, `country_id`),
INDEX `from_to_index` (`ipfrom`, `ipto`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB;

Not sure why the “from_to_index” is there – seems redundant to me. But anyway, the EXPLAIN query looks like this

EXPLAIN SELECT *
        FROM track_report t, countries_ip ip
        WHERE t.ip BETWEEN ip.ipfrom AND ip.ipto

and the result of the EXPLAIN is as follows:

id  select_type table   type    possible_keys   key key_len ref rows    Extra
1   SIMPLE  t   ALL getwebmaster    NULL    NULL    NULL    36291   
1   SIMPLE  ip  ALL PRIMARY,from_to_index   NULL    NULL    NULL    153914  Range checked for each record (index map: 0x3)

As you can see, the PRIMARY KEY from the countries_ip table isn’t being used and so the query takes a LONG time (countries_ip has over 150k records)

I’m probably missing something simple, but any advice would be appreciated on how I can optimize this query. Thanks in advance.

Answer 1

It might help to define an index on track_report.ip. See SQL Fiddle.

I modified the where clause to do an explicit comparison, and now it uses the from_to_index.

SELECT ip
FROM track_report t, countries_ip ip
where t.ip >= ip.ipfrom and t.ip <= ip.ipto

See SQL Fiddle.