Commented by: chedek (chedek2)

The strangiest thing is that the query:

for execute statement (' select s.cod,s.num, http://s.name,sum(g.summa) from sch s
left join getschdet(s.cod,:datedoc1 ,:datedoc2,0,0,0,0,0,0,0,0,0,0,0,1,3) g on 1=1
where s.num in (''50'',''51'') and s.udl<>''У'' and s.root=1
and not exists (select s2.cod from sch s2 where s2.prevcod=s.cod)
group by 1,2,3') (datedoc1 := :datedoc, datedoc2 := :datedoc)

doesn't work too with same preprocess error.

Commented by: @hvlad

chedek, next time, *please*, post complete script, such as

recreate table sch (cod int, num int, name int, prevcod int, udl char(1), root int);

create or alter procedure getschdet(cod int, datedoc date, datedoc2 date,
p1 int, p2 int, p3 int, p4 int, p5 int, p6 int,
p7 int, p8 int, p9 int, p10 int, p11 int, p12 int, p13 int)
returns (summa int)
as
begin
suspend;
end;

execute block as
declare datedoc date;
declare cod int;
declare num int;
declare name int;
declare summa int;
begin
for execute statement (
' select s.cod,s.num, http://s.name,sum(g.summa) from sch s
left join getschdet(s.cod,:datedoc ,:datedoc,0,0,0,0,0,0,0,0,0,0,0,1,3) g on 1=1
where s.num in (''50'',''51'') and s.udl<>''У'' and s.root=1
and not exists (select s2.cod from sch s2 where s2.prevcod=s.cod)
group by 1,2,3') (datedoc := :datedoc)
into :cod, :num, :name, :summa
do exit;
end

Commented by: @hvlad

Changed description by more exact one

Commented by: @pcisar

QA test added.