different between || and && in a statement

Hi,

I hope theis is the last question for the next time:

1st statement:

SELECT (sum(case when dict.word = 'museum' then 1 else 0 end) 
&& sum(case when dict.word = 'immer' then 1 else 0 end)) as qu , dict.url_id
^^             FROM dict, url 
             WHERE url.rec_id = dict.url_id
                   AND url.url LIKE '%%' 
                   AND dict.word in ('museum','immer') 
             GROUP BY dict.url_id  
             HAVING sum(case when dict.word = 'museum' then 1 else 0 end) && 
sum(case when dict.word = 'immer' then 1 else 0 end) > 0                  ^^

The result is:

ERROR:  Unable to identify an operator '&&' for types 'int4' and 'int4'
        You will have to retype this query using an explicit cast

but if a do it with :

SELECT (sum(case when dict.word = 'museum' then 1 else 0 end)
|| sum(case when dict.word = 'immer' then 1 else 0 end)) as qu , dict.url_id
^^             FROM dict, url
             WHERE url.rec_id = dict.url_id
                   AND url.url LIKE '%%'
                   AND dict.word in ('museum','immer')
             GROUP BY dict.url_id
             HAVING sum(case when dict.word = 'museum' then 1 else 0 end) || 
sum(case when dict.word = 'immer' then 1 else 0 end) > 0                  ^^

.... all is OK

Whats the different between the logical expression && and || and is there
a way to get && working?

Thanks for any hints. I hope the isn't a stupid question.

Christian

-- 
 Christian Guenther                              Kunsthistoriker 
 Fax: +49 030 4464152             E-mail: cg@kunst-und-kultur.de
 Tel: +49 030 4442931                http://kunst-und-kultur.de/
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