Question

我有一个案例，我需要在每个函数变量的连接中运行不同的查询

目前我的功能为：

CREATE OR REPLACE FUNCTION a(type_f boolean)
  RETURNS SETOF rowtypes AS
$$
declare row rowtypes ;
begin   
....
select...
from..
left join (select pp.a, avg(ppp.priceusd) as avgpricetf
           from pp
           join p on (p.b=pp.b)
           join (...) as ppp on (pp.c=p.c)
           group by pp.a) tfquery on (tfquery.a=main.a)
....
end;
$$
  LANGUAGE plpgsql VOLATILE

这很好用。

我想修改它，以便type_f=True此查询将在原始查询的连接instad中运行：

left join (select pp.a,p.d, avg(ppp.priceusd) as avgpricetf
           from pp
           join p on (p.b=pp.b)
           join (...) as ppp on (pp.c=p.c)
           group by pp.a,p.d) tfquery on (tfquery.a=main.a and tfquery.d=main.d)

正如您所看到的那样，查询的更改以及连接本身的条件也是如此。

Basicly ：

type_f=False时：

left join (select pp.a, avg(ppp.priceusd) as avgpricetf
           from pp
           join p on (p.b=pp.b)
           join (...) as ppp on (pp.c=p.c)
           group by pp.a) tfquery on (tfquery.a=main.a)

当： type_f=True做：

left join (select pp.a,p.d, avg(ppp.priceusd) as avgpricetf
           from pp
           join p on (p.b=pp.b)
           join (...) as ppp on (pp.c=p.c)
           group by pp.a,p.d) tfquery on (tfquery.a=main.a and tfquery.d=main.d)

我该怎么做？

Answer 1

您可以使用这样的逻辑来消除查询的所有可读性并获得预期结果：

Select *
from A
left outer join
   ( select * from B where type_f
     union all
     select *, A.field from C where not type_f
   ) X
on X.n = A.n and X.field = A.field
....

使用PostgreSQL条件连接查询

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