表大小
24943*24943
1.原语句
SELECT A.ID1,A.ID2,A.relation FROM element_relations as A where ID1= 17 or ID2=17 order by relation DESC limit 300;
分别建立ID1,和ID2的索引
查看索引情况
索引id1，id2未用上
查询时间
查询时间
2.使用union all
(SELECT A.ID1,A.ID2,A.relation FROM element_relations as A where ID1= 1 order by relation DESC limit 300) union all (SELECT A.ID1,A.ID2,A.relation FROM element_relations as A where ID2= 1 order by relation DESC limit 300) order by relation DESC limit 300;
查看索引情况
查询时间
效果并不理想
3.重新建立索引
索引1：使用id1和relation联合索引
索引2：使用id3和relation联合索引
使用语句1
查看索引
查询时间
使用语句二 order by
索引情况
查询时间
