MySQL explain filtered column jumping 4,100 with index

Question

My Query:

EXPLAIN EXTENDED SELECT  `artwork`.`id` ,  `artwork`.`added` 
FROM  `artwork` 
ORDER BY  `artwork`.`added` DESC 
LIMIT 0 , 6

When I added an index on "added" to avoid using filesort and use index instead the output of explained went from

id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE artwork ALL NULL NULL NULL NULL 302 100.00 Using filesort

to

id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE artwork index NULL added 4 NULL 6 5033.33  

and I'm concerned about the filtered going up approximently 4,100 - I can't find on Google what filtered means

Answer 1

Hey, it's actually good news. It shows how many rows your limitations are removing from the result set. In this case, that would be your LIMIT statement. See the manual:

The filtered column indicates an estimated percentage of table rows that will be filtered by the table condition. That is, rows shows the estimated number of rows examined and rows × filtered / 100 shows the number of rows that will be joined with previous tables. This column is displayed if you use EXPLAIN EXTENDED.