Hello.
I have following table schema:
CREATE TABLE tbl (
`fld1` varchar(32) character set utf8 NOT NULL default '',
`fld2` bigint(20) default NULL,
`fld3` mediumtext character set utf8,
`fld4` tinyint(4) NOT NULL default '0',
`fld5` varchar(32) character set utf8 default NULL,
`fld6` text character set utf8,
`fld7` varchar(32) character set utf8 default NULL,
`fld8` bigint(20) NOT NULL default '0',
`fld9` varchar(32) character set utf8 default NULL,
`fld10` varchar(32) NOT NULL default '',
PRIMARY KEY (`fld1`),
UNIQUE KEY `fld5` (`fld5`),
KEY `fld10` (`fld10`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1 ;
If I do a explain of query:
select distinct fld10 from tbl where fld4=2;
it says me:
"1" "SIMPLE" "tbl" "ALL" \N \N \N \N "13" "Using where; Using temporary"

The query returns me an empty record set. Because there are currently no records with fld=4.
Now my question is: why does MySQL need to create a temporary table?
In addition MYSQL creates the tmp table on disk, which is
slow.
tmp_table_size and max_heap..is 512M

Hope somebody can help me...
Regards