mysql 3个表关联时查询时的优化

Question

一共三张表tips,tippings,comments。tippings 是中间表。tips 和 comments 是多对多的关系。tips只有两列：id,name
tippings 的create语句：
[code="sql"]
CREATE TABLE tippings (
id INT(11) NOT NULL AUTO_INCREMENT,
tip_id INT(11) NULL DEFAULT NULL,
tippable_id INT(11) NULL DEFAULT NULL,
tipper_id INT(11) NULL DEFAULT NULL,
tipper_type VARCHAR(255) NULL DEFAULT NULL,
tippable_type ENUM('Post','Comment') NULL DEFAULT NULL,
context ENUM('tips') NULL DEFAULT NULL,
created_at DATETIME NULL DEFAULT NULL,
PRIMARY KEY (id),
INDEX index_tippings_on_tip_id (tip_id),
INDEX index_tippings_on_tippable_id_and_tippable_type_and_context (tippable_id, tippable_type, context),
INDEX index_cttt (context, tippable_type, tippable_id, tip_id)
)
[/code]
查询语句为
[code="sql"]
SELECT tips.*, COUNT(*) AS count FROM tips LEFT OUTER JOIN tippings
ON tips.id = tippings.tip_id INNER JOIN
comments ON comments.id = tippings.tippable_id WHERE (tippings.tippable_type
= 'Comment') GROUP BY tips.id, tips.name HAVING COUNT(*) > 0 ORDER BY
count desc LIMIT 75;
[/code]
tippings 目前800多万条记录。
查询速度太慢
各位帮忙看看能不能更好的优化下

Answer 1

额 错了 http://asyty.iteye.com/blog/1202943