Question

我有这个索引：

alter table wx_cbmessage add index main_query (cbm_owner_id,cbm_status,cbm_date,cbm_notification_date);

这个查询：

SELECT SQL_CALC_FOUND_ROWS ... 
FROM `wx_cbmessage` `msg` FORCE INDEX (main_query) 
    LEFT JOIN wx_user `from` ON cbm_from_user_id=from.login 
WHERE `cbm_owner_id`='username' 
    AND cbm_date <= 1431448013 
    AND (`cbm_notification_date`=0 OR cbm_notification_date <= 1431448013) 
    AND `cbm_status`=1 
ORDER BY `cbm_date` DESC 
LIMIT 25

是否有cbm_notification_date作为索引的一部分？它可以被利用吗？

前两列只是完全匹配，但我不知道MySQL是否可以对多个范围搜索做任何事情。

Answer 1

Please qualify the column names with the table aliases. Without knowing what column is what table, I have to guess at how to advise.

Two ranges -- Won't be used.

EXPLAIN failing to explain -- Try List<Part>.

I recommend this (Since the columns are all in the same table):

EXPLAIN FORMAT=JSON SELECT ...

It can be used for 2 constants and a range. And it can for the INDEX(cbm_owner_id, cbm_status, cbm_date). The optimizer has no good way to pick which one to use.

ORDER BY

cannot use an index because of the combination of (`cbm_notification_date`=0 OR cbm_notification_date <= 1431448013) and 'range'. OR is equivalent to (x=1 OR x=3), which is better than a range, although not quite as good as a constant.

可以在多个＆＃39;范围内进行索引。列被利用？

1 个答案: