select * from table where field1 in ['A..'z']

select * from table where ['A..'z'] in field1

CREATE PROCEDURE EN_RU (
   s varchar(50) character set cyrl)
returns (
   idx integer)
as
declare variable i integer;
declare variable ch char(1) character set cyrl;
declare variable en varchar(30);
declare variable ru varchar(34);
begin
EN='ABCDEFGHIJKLMNOPQRSTUVWXYZ';
RU='АБВГДЕЁЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯ';
I=1;
while (i<=strlen(:S)) do
begin
 Ch = substring(:S from :i for 1);
 if ((:EN containing :Ch) or (:RU containing :Ch)) then
 begin
   IDX=:I;
   break;
   end
 I=:I+1;
 end
 suspend;
end

SELECT  T1.*
FROM    table1 T1
WHERE  (T1.FIELD1 SIMILAR TO '[A-z]')
     OR  (T1.FIELD1 SIMILAR TO '[А-я]')

SELECT  T1.*
FROM    table1 T1
WHERE  (T1.FIELD1 SIMILAR TO '[0-9]')

BEGIN
USERTYPE = 'MEMBER';
NUM='0123456789';
I=1;
Ch = '/';
while ((ch <> '')and(usertype = 'MEMBER')) do
begin
Ch = substring(:S from :i for 1);
if ((:NUM containing :Ch)) then
begin
  USERTYPE = 'NUM';
  break;
end
I=:I+1;
end
suspend;
END

Invalid token.
Dynamic SQL Error.
SQL error code = -104.
Token unknown - line 16, column 25.
:.

substr