>>>> why does mysql use group_id index ? >>> because in this case group_id would be faster than user_id >> but in fact group_id is very slow (51.21 sec), user_id is (0.00 sec) > > ok, at least MySQL does think so I know, but I what I really want to know is how does mysql think so ? > >>>> how to let mysql choose user_id as an index ? what's the mean of 'rows' ? >>> valid rows after applying the WHERE to this index >> the result is empty set, if what you said is true, then the rows must be >> 0 ? > > no, not the final result, only for this index > > read about EXPLAIN in the MySQL manual > > http://dev.mysql.com/doc/refman/5.0/en/using-explain.html I has read it , and it described like what you said, I don't really know what is the mean of 'only for this index', I tried 'select count(*) from photo where group_id=0 and album_id!=0,' ant it get a huge number, but not the value of rows. > > -- > Sebastian > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] > >
-- Thanks & Regards Changying Li -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
