PostgreSQL的缩小数据集优化过程一例

概述小黄同学拿过来一句SQL问我，看看能不能优化，看了下，数据量不是很大，查询还不算很复杂。以下是记录优化过程： DB：PostgreSQL 9.1 OS：CentOS 6 count(d_personal_report_view) ~ 9K条，涉及金额数量的字段类型为numeric(9,2)类型 原始SQL: select distinct c.doctor_name,c.department_na 小黄同学拿过来一句sql问我，看看能不能优化，看了下，数据量不是很大，查询还不算很复杂。以下是记录优化过程：

DB：Postgresql 9.1
OS：CentOS 6
count(d_personal_report_vIEw) ~ 9K条，涉及金额数量的字段类型为numeric(9,2)类型

原始sql:

select distinct c.doctor_name,c.department_name,c.hospital_ID,c.hospital_name,c.part_hospital_name,t.* from d_personal_report_vIEw c,(       select dc.part_hospital_ID,dc.department_ID,dc.doctor_ID,coalesce(sum(coalesce(dc.surgery_amount,'0.0')),'0.0') as surgery_amount,sum(coalesce(dc.surgery_quantity,0)) as surgery_quantity,coalesce(sum(coalesce(dc.repair_amount,'0.0') as repair_amount,sum(coalesce(dc.repair_quantity,0)) as repair_quantity,coalesce(sum(coalesce(dc.orthod_amount,'0.0') as orthod_amount,sum(coalesce(dc.orthod_quantity,0)) as orthod_quantity,coalesce(sum(coalesce(dc.radiation_amount,'0.0') as radiation_amount,sum(coalesce(dc.radiation_quantity,0)) as radiation_quantity,coalesce(sum(coalesce(dc.teethcln_amount,'0.0') as teethcln_amount,sum(coalesce(dc.teethcln_quantity,0)) as teethcln_quantity,coalesce(sum(coalesce(dc.crop_amount,'0.0') as crop_amount,sum(coalesce(dc.crop_quantity,0)) as crop_quantity,coalesce(sum(coalesce(dc.assay_amount,'0.0') as assay_amount,sum(coalesce(dc.assay_quantity,0)) as assay_quantity,coalesce(sum(coalesce(dc.drugs_amount,'0.0') as drugs_amount,sum(coalesce(dc.drugs_quantity,0)) as drugs_quantity,coalesce(sum(coalesce(dc.regist_amount,'0.0') as regist_amount,sum(coalesce(dc.regist_quantity,0)) as regist_quantity,coalesce(sum(coalesce(dc.others_amount,'0.0') as others_amount,sum(coalesce(dc.others_quantity,0)) as others_quantity,coalesce(sum(surgery_amount + repair_amount + orthod_amount + radiation_amount + teethcln_amount + crop_amount + assay_amount + drugs_amount + regist_amount + others_amount),'0.0') as totalRowAmount,coalesce(sum(surgery_quantity + repair_quantity + orthod_quantity + radiation_quantity + teethcln_quantity + crop_quantity + assay_quantity + drugs_quantity + regist_quantity + others_quantity),0) as totalRowQuantity from d_personal_report_vIEw dcwhere 1=1 group by dc.part_hospital_ID,dc.doctor_ID order by dc.part_hospital_ID,dc.doctor_IDlimit 10 offset 0) as t   where c.part_hospital_ID=t.part_hospital_ID and c.department_ID=t.department_ID and c.doctor_ID=t.doctor_ID order by t.part_hospital_ID,t.department_ID,t.doctor_ID;

一.分析
看其结果是要取10条不同的数据做报表展示，用了同一张表做了两次关联，没有涉及查询条件，索引效果不大。分析这个sql好不好，先看一下执行计划


二.优化过程
1.取消两张表的关联，只取一次查询 优化后的sql：

select  dc.doctor_name,dc.department_name,dc.hospital_name,dc.part_hospital_name,dc.part_hospital_ID,0) as totalRowQuantity from d_personal_report_vIEw dcwhere 1=1 group by dc.doctor_name,dc.doctor_IDlimit 10 offset 0

查看其执行计划:


2.其执行计划中的cost还是有点高，再次优化 postgresql中的sum会自动把null值替换成0，并考虑到不会存入''或者' '等空值，故可以去掉里面的coalesce转换函数。
优化后的sql:

select  dc.doctor_name,sum(dc.surgery_amount) as surgery_amount,sum(dc.surgery_quantity) as surgery_quantity,sum(dc.repair_amount) as repair_amount,sum(dc.repair_quantity) as repair_quantity,sum(dc.orthod_amount) as orthod_amount,sum(dc.orthod_quantity) as orthod_quantity,sum(dc.radiation_amount) as radiation_amount,sum(dc.radiation_quantity) as radiation_quantity,sum(dc.teethcln_amount) as teethcln_amount,sum(dc.teethcln_quantity) as teethcln_quantity,sum(dc.crop_amount) as crop_amount,sum(dc.crop_quantity) as crop_quantity,sum(dc.assay_amount) as assay_amount,sum(dc.assay_quantity) as assay_quantity,sum(dc.drugs_amount) as drugs_amount,sum(dc.drugs_quantity) as drugs_quantity,sum(dc.regist_amount) as regist_amount,sum(dc.regist_quantity) as regist_quantity,sum(dc.others_amount) as others_amount,sum(dc.others_quantity) as others_quantity,sum(surgery_amount + repair_amount + orthod_amount + radiation_amount + teethcln_amount + crop_amount + assay_amount + drugs_amount + regist_amount + others_amount) as totalRowAmount,sum(surgery_quantity + repair_quantity + orthod_quantity + radiation_quantity + teethcln_quantity + crop_quantity + assay_quantity + drugs_quantity + regist_quantity + others_quantity) as totalRowQuantity from d_personal_report_vIEw dcwhere 1=1 group by dc.doctor_name,dc.doctor_IDlimit 10 offset 0

查看执行计划：

结果是一样的，从侧面也反映出Postgresql的这个内部转换函数消耗不是很大

3.缩小查询基数，提升查询性能 之前的查询语句都是先全表扫描基础表并按规则排序和分组，最后才取10条，其实从另一个角度可以先取一定数量的数据，不用全表，但是一般可满足数据结果的不同，然后再取10条出来。

优化后的sql

select dc.doctor_name,sum(surgery_quantity + repair_quantity + orthod_quantity + radiation_quantity + teethcln_quantity + crop_quantity + assay_quantity + drugs_quantity + regist_quantity + others_quantity) as totalRowQuantity from (select * from d_personal_report_vIEw limit 1000) as dcgroup by dc.doctor_name,dc.doctor_IDlimit 10 offset 0

此时再来看执行计划： 效果有了显著的提升，特别是遇到基础表快速膨胀的时候，响应时间也快了很多。

此方法对其他DB也适用，但是要与业务结果相匹配。 总结

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