Problem in dynamic query execution in plpgsql

Hai all,
I Have a problem,I have a plpgsql function
==================================

CREATE OR REPLACE FUNCTION
function_to_get_ticket_wise_sales(VARCHAR,VARCHAR) RETURNS SETOF RECORD AS '

DECLARE

dat_from_date ALIAS FOR $1;

dat_to_date ALIAS FOR $2;

dat_from DATE;

dat_to DATE;

vchr_query VARCHAR(1000);

r RECORD;

BEGIN

dat_from := to_date(dat_from_date, ''DD MM YYYY'');

dat_to := to_date(dat_to_date,''DD MM YYYY'');

vchr_query := ''SELECT
vchr_ticket_number,dat_ticket_issue,vchr_pax_name,vchr_sector,

dbl_market_fare_inv,
dbl_special_fare_inv,dbl_std_commn_percentage_inv,vchr_our_lpo,

dbl_market_fare_inv AS
flt_claim,dbl_supplier_amount,dbl_service_charge,dbl_selling_price,vchr_inv_document_number,fk_bint_supplier_id,chr_supplier_type,
vchr_airline_numeric_code, vchr_account_code_inv , vchr_account_name_inv
FROM tbl_ticket WHERE dat_ticket_issue BETWEEN ''|| dat_from || '' AND '' ||
dat_to || '' ;

RAISE NOTICE ''Query : % '',vchr_query;

vchr_query := vchr_query || '' AND (vchr_our_lpo = '' '' OR vchr_our_lpo =
"VS") '';

FOR r in EXECUTE vchr_query LOOP

RETURN NEXT r;

END LOOP;

RETURN;

END

' language 'plpgsql';

==================================

my problems are:

1 problem : in RAISE NOTICE query string is print like this,

SELECT vchr_ticket_number,dat_ticket_issue,vchr_pax_name,vchr_sector,

dbl_market_fare_inv,
dbl_special_fare_inv,dbl_std_commn_percentage_inv,vchr_our_lpo,

dbl_market_fare_inv AS
flt_claim,dbl_supplier_amount,dbl_service_charge,dbl_selling_price,vchr_inv_document_number,fk_bint_supplier_id,chr_supplier_type,
vchr_airline_numeric_code, vchr_account_code_inv , vchr_account_name_inv
FROM tbl_ticket WHERE dat_ticket_issue BETWEEN 2008-04-01 AND 2008-07-10

when $1 = '2008-04-01' and $2 = '2008-04-10' , but i dont get the required
result.

I think that i will get the result if my query string will be like this(ie
dates in single quote),

:

SELECT vchr_ticket_number,dat_ticket_issue,vchr_pax_name,vchr_sector,

dbl_market_fare_inv,
dbl_special_fare_inv,dbl_std_commn_percentage_inv,vchr_our_lpo,

dbl_market_fare_inv AS
flt_claim,dbl_supplier_amount,dbl_service_charge,dbl_selling_price,vchr_inv_document_number,fk_bint_supplier_id,chr_supplier_type,
vchr_airline_numeric_code, vchr_account_code_inv , vchr_account_name_inv
FROM tbl_ticket WHERE dat_ticket_issue BETWEEN '2008-04-01' AND '2008-07-10
'

How i can put the dates in single quote in a dynamic query string?

2 problem:

next problem is i have a varchar variable vchr_our_lpo how I can check is it
containn an empty string or characters in a dynamic query string

I tried different methods like,

vchr_query :='' (vchr_our_lpo = '' '' OR vchr_our_lpo = "VS") '';

str_temp2:= ''VS'';

vchr_query := '' (vchr_our_lpo = '' '' OR vchr_our_lpo = %) '',str_temp2;

but all failed

How I can solve these problem in a dynamic query string?.pls help me with a
suitable example

thanks in advance:

Anoop G