Quotes, double quotes...

Hi all,

I have a problem with quotes which I can't find a solution.

Inside a query string I have another query string; I used for the later
double quotes, but it is still complaining

The problem is with the function pgr_drivingdistance (from pgrouting
extension).

The code is the following:

-----------------------------------------------------
DO $$
DECLARE
i integer;
BEGIN
FOR i IN (select nn from numeros)
LOOP
EXECUTE
'create table contagio' || i || ' as
SELECT *
FROM pgr_drivingdistance("
SELECT gid AS id,
source,
target,
tempo::float8 AS cost
FROM lisboa",
' || i || ' ,
30,
false,
false)
';
END LOOP;
END;
$$;
------------------------------------------------------

I get the following error:
-----------------------------------------------------
NOTICE: identifier "
SELECT gid AS id,
source,
target,
tempo::float8 AS cost
FROM lisboa" will be truncated to "
SELECT gid AS id,
source,
target,
"
CONTEXT: SQL statement "create table contagio18 as
SELECT *
FROM pgr_drivingdistance("
SELECT gid AS id,
source,
target,
tempo::float8 AS cost
FROM lisboa",
18 ,
30,
false,
false)
"
PL/pgSQL function "inline_code_block" line 7 at EXECUTE statement

ERROR: column "
SELECT gid AS id,
source,
target,
" does not exist
LINE 3: FROM pgr_drivingdistance("
^
QUERY: create table contagio18 as
SELECT *
FROM pgr_drivingdistance("
SELECT gid AS id,
source,
target,
tempo::float8 AS cost
FROM lisboa",
18 ,
30,
false,
false)

CONTEXT: PL/pgSQL function "inline_code_block" line 7 at EXECUTE statement

********** Error **********

ERROR: column "
SELECT gid AS id,
source,
target,
" does not exist
SQL state: 42703
Context: PL/pgSQL function "inline_code_block" line 7 at EXECUTE statement
-------------------------------------------------------------------------------------------

I suspect the solution is probably simple; yet, I can't get it.

Thanks in advance for any help.

António