Index usage for ORDER BY / LIMIT?
I'd like to get the latest 30 dates from a table that could potentially have hundreds of thousands of rows. I thought that the index on the date column would provide enough information to allow MySQL to quickly get the data. But the way I read the EXPLAIN plan, MySQL is doing a table scan (rows=5415).
Am I misreading the EXPLAIN plan? Is there a way to tell whether MySQL is scanning just the index or the actual table? I'm hoping to avoid adding a derived column just to get this query to run optimally.
I'd appreciate any help I can get.
Thanks,
Boris
---------------
mysql> EXPLAIN SELECT date FROM my_table ORDER BY date LIMIT 30 \G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: mail_item
type: index
possible_keys: NULL
key: i_date
key_len: 8
ref: NULL
rows: 5415
Extra: Using index
1 row in set (0.00 sec)
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Index usage for ORDER BY / LIMIT?
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June 14, 2005 11:34AM
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