目录

1、推荐文章与标签关系联表查询优化

目的查询带有指定标签的所有文章信息

sql写法1

SELECT DISTINCT qa.id as id,`title`,`banner`,`stime`,`etime`,`status`,`desc` FROM qu_article qa JOIN qu_article_tag as qat ON qa.id=qat.a_id and qat.tag_id in(1057,1051,1044,1043,1035,1034,1015,1014,1006,999,988,983,980,975,974,973,968,964,946,944,938,936,913,894,874,867,860,859,851,831,829,822,813,767,760,751,748,723,720,719,715,714,702,629,624,622,620,618,610,598,593,580,561,558,552,537,536,531,521,516,513,512,505,494,488,487,483,453,449,447,435,433,429,428,416,411,403,402,392,383,381,374,368) ORDER BY qa.order_num desc LIMIT 10,10

#执行：3.096s

#Explain分析结果：

idselect_typetabletypepossible_keyskeykey_lenrefrowsExtra

1SIMPLEhatrangeidx_article_id,idx_tag_ididx_tag_id4\N31112Using where; Using temporary; Using filesort

1SIMPLEhaeq_refPRIMARYPRIMARY4qing.qat.article_id1

sql写法2

explain SELECT `id`,`title`,`banner`,`stime`,`etime`,`status`,`desc` FROM qu_article where id in(select a_id from qu_article_tag where tag_id in(1057,1051,1044,1043,1035,1034,1015,1014,1006,999,988,983,980,975,974,973,968,964,946,944,938,936,913,894,874,867,860,859,851,831,829,822,813,767,760,751,748,723,720,719,715,714,702,629,624,622,620,618,610,598,593,580,561,558,552,537,536,531,521,516,513,512,505,494,488,487,483,453,449,447,435,433,429,428,416,411,403,402,392,383,381,374,368)) order by order_num desc limit 10;

#执行时间：0.08s

#Explain分析结果：

idselect_typetabletypepossible_keyskeykey_lenrefrowsExtra

1PRIMARYqu_articleindex\Nidx_order_num4\N10Using where

2DEPENDENT SUBQUERYqu_article_tagindex_subqueryidx_article_id,idx_tag_ididx_article_id4func1Using where

注：文章推荐表与文章标签关系表，两张表的记录不大(不超10万条)，不需要采用join，join会产生临时表及内存的文件排序，将join改为子查询，可以充分利用各自表的索引与主键查询与排序。