优化DB2查询加入

Question

我有复杂的查询：

select rma.RELATION_MANAGER_ID, 
     rm.ORG_STRUCTURE_ID, 
     rm.RELATIONSHIP_MANAGER_NM, 
     count(distinct ppa.PARTY_ID) as count_party 
from RELATIONSHIP_MANAGER rm --15808 row 
join RELATIONSHIP_MANAGER_MARKET rmm --1560 row 
    on rm.RELATIONSHIP_MANAGER_ID = rmm.RELATIONSHIP_MANAGER_ID 
     and rmm.INCLUDE_IN_REPORT = 'Y' 
join MARKET_SEGMENT rm_ms --4 row 
    on rmm.MARKET_SEGMENT_ID = rm_ms.MARKET_SEGMENT_ID 
     and rm_ms.MARKET_SEGMENT = '01' 
join RELATIONSHIP_MANAGER_ALLOCATION rma --61349 row 
    on rm.RELATIONSHIP_MANAGER_ID = rma.RELATIONSHIP_MANAGER_ID 
join CMD_PARTY_PORTFOLIO_ALLOCATION ppa --3114096 row 
    on ppa.PORTFOLIO_ID = rma.PORTFOLIO_ID 
join person ps --3112575 row 
    on ps.IS_DELETED != 1 and ppa.party_id = ps.party_id 
join PARTY p --3114146 row 
    on ppa.party_id=p.party_id 
join MARKET_SEGMENT ms --4 row 
    on p.MARKET_SEGMENT_ID = ms.MARKET_SEGMENT_ID and ms.MARKET_SEGMENT = '01' 
    where rm.IS_CM = 1 and rm.IS_DELETED != 1 
group by rm.RELATIONSHIP_MANAGER_NM, rma.RELATIONSHIP_MANAGER_ID, rm.ORG_STRUCTURE_ID 

表列存在索引：

rm.RELATIONSHIP_MANAGER_ID, 
rmm.RELATIONSHIP_MANAGER_ID, 
rmm.MARKET_SEGMENT_ID, 
rm_ms.MARKET_SEGMENT_ID, 
rma.RELATIONSHIP_MANAGER_ID, 
ppa.PORTFOLIO_ID, 
rma.PORTFOLIO_ID, 
ppa.party_id, 
ps.party_id, 
p.party_id, 
p.MARKET_SEGMENT_ID, 
ms.MARKET_SEGMENT_ID 

表PARTY，人有〜1-3百万行，查询 运行时间〜 20秒。我的评论

join MARKET_SEGMENT ms 
on p.MARKET_SEGMENT_ID = ms.MARKET_SEGMENT_ID --and ms.MARKET_SEGMENT = '01' 

查询运行时间变成了~3秒。 请解释为什么发生这种情况？ 解释计划不帮我..我如何优化查询？

编辑： 平台是针对z/OS V9.7， 增加表的大小DB2

EDIT2：解释计划显示，第一总是加入表的小尺寸

Answer 1

只是为了咧嘴笑，看看这是否有任何区别：

WITH 
MktSeg(MARKET_SEGMENT_ID) AS 
(SELECT MARKET_SEGMENT_ID 
    FROM MARKET_SEGMENT 
    WHERE MARKET_SEGMENT = '01') 
select rma.RELATION_MANAGER_ID, 
     rm.ORG_STRUCTURE_ID, 
     rm.RELATIONSHIP_MANAGER_NM, 
     count(distinct ppa.PARTY_ID) as count_party 
from RELATIONSHIP_MANAGER rm --15808 row 
join RELATIONSHIP_MANAGER_MARKET rmm --1560 row 
    on rm.RELATIONSHIP_MANAGER_ID = rmm.RELATIONSHIP_MANAGER_ID 
     and rmm.INCLUDE_IN_REPORT = 'Y' 
join MktSeg rm_ms --4 row 
    on rmm.MARKET_SEGMENT_ID = rm_ms.MARKET_SEGMENT_ID 
join RELATIONSHIP_MANAGER_ALLOCATION rma --61349 row 
    on rm.RELATIONSHIP_MANAGER_ID = rma.RELATIONSHIP_MANAGER_ID 
join CMD_PARTY_PORTFOLIO_ALLOCATION ppa --3114096 row 
    on ppa.PORTFOLIO_ID = rma.PORTFOLIO_ID 
join person ps --3112575 row 
    on ps.IS_DELETED != 1 and ppa.party_id = ps.party_id 
join PARTY p --3114146 row 
    on ppa.party_id=p.party_id 
join MktSeg ms --4 row 
    on p.MARKET_SEGMENT_ID = ms.MARKET_SEGMENT_ID 
WHERE rm.IS_CM = 1 AND rm.IS_DELETED != 1 
group by rm.RELATIONSHIP_MANAGER_NM, rma.RELATIONSHIP_MANAGER_ID, 
     rm.ORG_STRUCTURE_ID, rma.RELATION_MANAGER_ID 

请注意，我已经添加了一个项目到Group By子句。