Problem with pg_index.

Hi the list !
I'm new to this list.
I've tried to write a sql query to get all the fields of a table and to
have mentionned is a field can be null or not, and if a field is a key
or not.
Before showing the query I send, let me tell you that I'm running
postgre v7.1.2 on a SuSE Linux 6.4 box, and that everything works fine
but this query.
Here it is :

select pg_class.oid, pg_attribute.attname, pg_attribute.attbyval, pg_attribute.attnotnull 
from pg_class, pg_attribute, pg_index 
where relname='essai2'and pg_attribute.attrelid=pg_class.oid and pg_attribute.attnum >0 and
pg_index.indrelid=pg_class.oidand pg_index.indkey[0] = pg_attribute.attnum 
 

This query doesn't work, the back-end answers Error : Invalid Command
name "0"...
What now ? I've checked out the online doc, and the archives of this
list (that's where I got pg_index.indkey[0] from), but nothing seems to
work, since pg_index.indkey seems to be an int2vector, and I found no
integrated function to check if a value is in this vector... Thanks for
your ideas and//or help.
-- 
David BOURIAUD
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