如何在简单的MySQL查询中设计索引/查询以避免文件排序？

Question

I have a table entrytable , that has the colums datum , username , status , status_spam_user , status_spam_system and text .

I want to select the content of the column text, from rows that have certain values for username , status , status_spam_user , status_spam_system . Since this can result in a long list of entries (>30'000) I want to limit the number of matching rows. Before I to that, the matching rows should be ordered by the column datum .

SELECT text
FROM entrytable
WHERE user = 'username' &&
`status` = '1' && (
    `status_spam_user` = 'no_spam'
    || (
        `status_spam_user` = 'neutral' &&
        `status_spam_system` = 'neutral'
    )
)
ORDER BY datum DESC
LIMIT 6430 , 10

I added two indices to the table:

• index_datum (datum)
• index_status_mit_spam (user, status, status_spam_user, status_spam_system)

For this query the index index_status_mit_spam is used. Since the index does not contain information of the column datum , the sorting has to be does separately (ie filesort). Is it possible to design my query/index in a way, that it is useful for the WHERE as well as for ORDER BY ?

Answer 1

在status_spam_user / status_spam_system上添加一个索引on (user, status, datum)索引因为OR条件（它被用于状态部分）而无法使用，并且必须在之前使用索引的所有先前部分按部分排序可以满足索引