原因分析1.当sql中的基表数据量过大，where条件中使用了or 关键字，即使条件中的字段已建索引，索引也是使用不上。因为用了or关键字，记录的查询没法通过某个确定的地址进行查询。从而走全表扫描，造成CPU、IO严重的性能问题,sql语句很长时间执行不出来。

解决方法1.将or两边关联的条件分别独立出来跟前面的select 内容进行组合，中间用union all进行数据的连接，如下所示： SELECT "TO"."FID""ID","TO"."FMATERIALID""T1.ID","T1"."FNUMBER""T1.NUMBER","T0"."FCOMPANYID""T2.ID","T2"."FNAME_L2""T2.NAME","T2"."FNAME_L1""T2.NAME_L1","T2"."FNAME_L2""T2.NAME_L2","T2".FNAME_L3""T2.NAME_L3","T2"."FNUMBER" "T2.NUMBER"FROM "T_BD_MATERIALCOMPANYINFO""T0" LEFT OUTER JOIN "T_BD_MATERIAL" "T1" ON"T0"."FMATERIALID" = "T1"."FID" LEFTOUTER JOIN "T_ORG_COMPANY" "T2" ON"T0"."FCOMPANYID" = "T2"."FID" WHERE((("T0"."FCOMPANYID" = :1 AND"T0"."FMATERIALID" = :2) AND("T0"."FSTATUS" <> :3))Union allSELECT"TO"."FID""ID","TO"."FMATERIALID""T1.ID","T1"."FNUMBER""T1.NUMBER","T0"."FCOMPANYID""T2.ID","T2"."FNAME_L2""T2.NAME","T2"."FNAME_L1""T2.NAME_L1","T2"."FNAME_L2""T2.NAME_L2","T2".FNAME_L3""T2.NAME_L3","T2"."FNUMBER" "T2.NUMBER"FROM "T_BD_MATERIALCOMPANYINFO""T0" LEFT OUTER JOIN "T_BD_MATERIAL" "T1" ON"T0"."FMATERIALID" = "T1"."FID" LEFTOUTER JOIN "T_ORG_COMPANY" "T2" ON "T0"."FCOMPANYID"= "T2"."FID" WHERE (("T0"."FCOMPANYID" = :4 AND"T0"."FMATERIALID" = :5) AND("T0"."FSTATUS" <> :6))Sql改造后，查看执行计划，cost消耗比之前少了很多，原基表全表扫描，现变成了走索引，如下图所示:

关键字or关键字造成全表扫描