我正在尝试将下面的join语句转换为pig。

from EXCH e
JOIN (select a,p, count(buyer) from EXCH group by a, p) sq on e.a = sq.a and e.p = sq.p
left outer join myimplocal i on e.a = i.a and e.p = i.p and e.f = i.f and i.imp > 0 and e.iswin = 1

目前，我有：

EXCH2 = FOREACH EXCH GENERATE a, p, buyer; 
EXCH2_groupby = GROUP EXCH2 BY (a, p); 
EXCH_alias_sq = FOREACH EXCH2_groupby GENERATE EXCH2.a, EXCH2.p, COUNT(EXCH2.buyer);
join_EXCH_and_EXCH_alias_sq = JOIN EXCH by (a, p), EXCH_alias_sq by (a, p);
myimplocal_filterby_imp_notZero = FILTER myimplocal BY imp > 0;

我应该过滤吗 e.iswin=1 在做左外连接之前？我应该用过滤器过滤吗 join_EXCH_and_EXCH_alias_sq ，然后在 myimplocal_filterby_imp_notZero 我的过滤器别名呢？
任何帮助都将不胜感激。