问题描述
全部，我想从这个查询中得到可靠的结果：
SELECT ..
FROM
(
SELECT
CO_CODE,REP.cua cua,PRD.PRODUCT_DESC,REGEXP_EXTRACT(B.rfbbn,'^(?:[^*]*\\*){2}([^*]*)',1) cllt,NVL(CCY_bbce,0) bbce,B.TYPE,A.conn_keyy
FROM
(
SELECT conn_keyy,ext_date FROM
(tablee.aa) A
)aaxyz
WHERE flag = 'Y'
)A
LEFT OUTER JOIN
tablee.B
ON A.conn_keyy = B.conn_keyy
LEFT OUTER JOIN (SELECT disTINCT * FROM tablee.cc) CPLCUR
ON CPLCUR.conn_keyy = A.conn_keyy
AND CPLCUR.cllt = REGEXP_EXTRACT(B.rfbbn,1)
AND CPLCUR.dtdt = '1999'
LEFT OUTER JOIN (SELECT disTINCT * FROM tablee.dd) CPLBAL
ON CPLBAL.conn_keyy = A.conn_keyy
AND CPLBAL.SEQUENCE = CPLCUR.SEQUENCE
AND CPLBAL.dtdt = '1999'
LEFT OUTER JOIN (SELECT disTINCT * FROM tablee.ee) CPLCCY
ON CPLCCY.conn_keyy = A.conn_keyy
AND CPLCCY.SEQUENCE = CPLCUR.SEQUENCE
AND CPLCCY.dtdt = '1999'
LEFT OUTER JOIN (SELECT disTINCT * FROM tablee.ff) CPLMOV
ON CPLMOV.conn_keyy = A.conn_keyy
AND CPLMOV.SEQUENCE = CPLCUR.SEQUENCE
AND CPLMOV.dtdt = '1999'
LEFT OUTER JOIN
(tablee.REP)REP
ON REP.relino = B.lnido
LEFT OUTER JOIN tablee.P PRD
ON PRD.PRODUCT_CODE = REGEXP_EXTRACT(A.conn_keyy,'[.]([^.]+)',1)
AND PRD.dtdt = '1999'
WHERE B.lnido LIKE 'PLCONS1%'
) rrvv;
仅供参考，A 的选择计数 (*) 约为 60,000
我只是想知道为什么我的查询结果变成了 15 亿.. 我错过了什么？操作left-outer-join时出现了什么问题？
解决方法
Join 可以重复行如果连接键在第二个表中不唯一，并且如果连接键在两个表中都不唯一，则会产生更多重复。
例如：
with
A as (
select 1 key,'one' name
union all
select 1 key,'two' name
),B as (
select 1 key,'two' name
)
select *
from A left join B on A.key=B.key
结果为四行，每个表只包含两行：
a.key a.name b.key b.name
1 one 1 one
1 one 1 two
1 two 1 one
1 two 1 two
如何找到重复的密钥：
select B.conn_keyy,count(*) cnt
from tablee.B
group by B.conn_keyy
having count(*)>1
order by cnt desc limit 100;
检查您要连接的每个表并决定您可以做什么：应用过滤、区分或添加更多连接键以进行连接（一对一或零）或（多对一或零)