About using plpgsql funciton variable as the table name

Greetings,

I met a question about how to use *function variable *as the *table
name* to select count(*) into an integer variable for the table.

CREATE OR REPLACE FUNCTION update_code_map(VARCHAR, VARCHAR) RETURNS
VARCHAR AS $$
DECLARE
*tableName ALIAS FOR $1*;
*rec_num INTEGER*;
query_value VARCHAR;
BEGIN
-- way 1
query_value := 'SELECT *INTO rec_num* COUNT(*) FROM ' || tableName
|| ' ';
EXECUTE query_value;

-- way 2
-- SELECT INTO rec_num COUNT(*) FROM tableName;
RAISE NOTICE 'There are % records in % table. ', rec_num,
tableName;

RETURN 'Populate ' || tableName || ' successfully!';
END;
$$ LANGUAGE plpgsql;
select update_code_map('code_map.dw_adm_dsn_map', '066');

I tried way 1 & way 2 , but neither of them worked. Could someone give
some clues?

Thanks a lot!
Emi