To reproduce:

cConnString ="DRIVER={PostgreSQL Unicode};DATABASE=postgres;"+ ;
   "SERVER=127.0.0.1;PORT=5432;UID=postgres;PWD=x;B9=0"
nconnh=SQLSTRINGCONNECT(cconnstring)
TEXT TO csql
CREATE table test ( test char(1));
insert into test values ('');
select CAST( 0 AS numeric(1)) from test
ENDTEXT

IF SQLEXEC(nconnh, csql)<0
  RETURN
  ENDIF

SELECT sqlresult
DISPLAY STRUCTURE TO FILE t
MODIFY FILE t

Observed: result table contains numeric(20,6) field
Expected: result table should contain numeric(1) type field

How to get expected result ?