SELECT citing.article_id as citing, lac_a.year, r.id_when_cited, cited_issue.country, citing.num_citations
FROM isi_lac_authored_articles as lac_a
JOIN isi_articles citing ON (lac_a.article_id = citing.article_id)
JOIN isi_citation_references r ON (citing.article_id = r.article_id)
JOIN isi_articles cited ON (cited.id_when_cited = r.id_when_cited)
JOIN isi_issues cited_issue ON (cited.issue_id = cited_issue.issue_id);
我有所有被加入的领域的索引。如何优化多个连接(已经有索引)的查询?
有什么我可以做的吗?我的表很大(大约有100万条记录,参考表有5亿条记录,文章表有25万条记录)。
这就是EXPLAIN不得不说:
+----+-------------+-------------+--------+--------------------------------------------------------------------------+---------------------------------------+---------+-------------------------------+---------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+--------+--------------------------------------------------------------------------+---------------------------------------+---------+-------------------------------+---------+-------------+
| 1 | SIMPLE | cited_issue | ALL | NULL | NULL | NULL | NULL | 1156856 | |
| 1 | SIMPLE | cited | ref | isi_articles_id_when_cited,isi_articles_issue_id | isi_articles_issue_id | 49 | func | 19 | Using where |
| 1 | SIMPLE | r | ref | isi_citation_references_article_id,isi_citation_references_id_when_cited | isi_citation_references_id_when_cited | 17 | mimir_dev.cited.id_when_cited | 4 | Using where |
| 1 | SIMPLE | lac_a | eq_ref | PRIMARY | PRIMARY | 16 | mimir_dev.r.article_id | 1 | |
| 1 | SIMPLE | citing | eq_ref | PRIMARY | PRIMARY | 16 | mimir_dev.r.article_id | 1 | |
+----+-------------+-------------+--------+--------------------------------------------------------------------------+---------------------------------------+---------+-------------------------------+---------+-------------+
5 rows in set (0.07 sec)
编辑:增加说明输出 – pocketfullofcheese 2012-03-12 07:52:00
你使用什么数据库类型?这是一个非常简单的SQL语句。你在使用myisam还是innodb? – 2012-03-12 07:57:28
myisam。它简单的SQL,但表格很大。 EXPLAIN输出的第一行有1M行...我可以通过分割我的查询来避免这种类型的事情吗?或者是其他东西? – pocketfullofcheese 2012-03-12 08:01:08