question 1

Hi, i have this query:
select * from libro where id_libro_key in (select id_libro from
libro_autore where id_auto
re in (select id_autore from autore where ((cognome = 'King' and nome =
'Stephen') OR (cog
nome = 'Clancy' and nome = 'Tom'))))\g
that return me this error:
ERROR:  There is no operator '=' for types 'int4' and 'varchar'
        You will either have to retype this query using an explicit cast,
        or you will have to define the operator using CREATE OPERATOR

but if I split the query in 2 part I obtain:
1)select id_libro from libro_autore where id_autore in (select id_autore
from autore where
 ((cognome = 'King' and nome = 'Stephen') OR (cognome = 'Clancy' and nome
= 'Tom')))\g
id_libro
--------
      11
      12
(2 rows)

2)esame=> select * from libro where id_libro_key in ( 11,12)\g
titolo      |id_libro|id_utente|collocazione|casa_edit|
data_publ|tipo|difetto|id_libro_ke
y
------------+--------+---------+------------+---------+----------+----+-------+-----------
-
It          |d1      |         |d1          |apo      |05-12-1940|   1|
|          1
1
Il talismano|s1      |         |d1          |aop2     |05-12-1985|   1|
|          1
2
(2 rows)

why I can not make the union/join ?
where I'm wrong ?
these are the table:
esame=> \d libro

Table    = libro
+----------------------------------+----------------------------------+-------+
|              Field               |              Type                |
Length|
+----------------------------------+----------------------------------+-------+
| titolo                           | varchar() not null               |
80 |
| id_libro                         | varchar() not null               |
10 |
| id_utente                        | int4                             |
4 |
| collocazione                     | varchar() not null               |
10 |
| casa_edit                        | varchar()                        |
20 |
| data_publ                        | date                             |
4 |
| tipo                             | int4                             |
4 |
| difetto                          | varchar()                        |
40 |
| id_libro_key                     | int4 not null default nextval (  |
4 |
+----------------------------------+----------------------------------+-------+


esame=> \d libro_autore

Table    = libro_autore
+----------------------------------+----------------------------------+-------+
|              Field               |              Type                |
Length|
+----------------------------------+----------------------------------+-------+
| id_libro                         | varchar() not null               |
10 |
| id_autore                        | int4 not null                    |
4 |
+----------------------------------+----------------------------------+-------+




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