Обсуждение: Related tables to a view
Hi I need a function which are able to return the underlying tables to a view. If I have a view which is a selection from field1 and field2 from table1 and field1 and field2 from table2. How can I make a selection which returns the relation for the fields in a way so I am able to se which field belongs to which table. SELECT * FROM pg_views WHERE viewname='TestView' will return the schema and the definition for me. SELECT * FROM pg_class WHERE relname = 'TestView' will return some oids etc. SELECT * FROM pg_attribute JOIN pg_class ON attrelid = pg_class.oid AND pg_class.relname='TestView' will return the fields including oids etc. But I just cant find out how to find the tables for each field. I hope someone are able to help me with this problem. Regards Jan Andersen
On Mon, Dec 25, 2006 at 10:52:03PM +0100, Jan Meyland Andersen wrote: > If I have a view which is a selection from field1 and field2 from table1 > and field1 and field2 from table2. > > How can I make a selection which returns the relation for the fields in a > way so I am able to se which field belongs to which table. You could query pg_depend to find out which tables and columns the view's rewrite rule depends on but that's not as specific as what you're requesting. I'm not aware of a way to associate a particular table column with a particular view column short of parsing the view definition or rule action; doing so would have to allow for the possibility of a view column deriving its value from an arbitrarily complex expression involving multiple tables, subqueries, etc. -- Michael Fuhr
> You could query pg_depend to find out which tables and columns the > view's rewrite rule depends on but that's not as specific as what > you're requesting. I'm not aware of a way to associate a particular > table column with a particular view column short of parsing the view > definition or rule action; doing so would have to allow for the > possibility of a view column deriving its value from an arbitrarily > complex expression involving multiple tables, subqueries, etc. Yes I'm aware of the "problem" about arbitrary or scalar values but this is not a problem in this specific case. If a field or value do not have a table reference then it is not needed in the resultset. I only need those values which have a direct connection to a table. Is the only possible way then to analyse the description field in pg_view? I was hoping for a more simple way to get the needed result. Regards Jan Andersen
> You could query pg_depend to find out which tables and columns the > view's rewrite rule depends on but that's not as specific as what > you're requesting. I'm not aware of a way to associate a particular > table column with a particular view column short of parsing the view > definition or rule action; doing so would have to allow for the > possibility of a view column deriving its value from an arbitrarily > complex expression involving multiple tables, subqueries, etc. I have been thinking the problem through again, and I think I am able to solve the problem if I just know which tables the view is using. But how do I get this information from the pg_depend table? Regards Jan
Try this query
select a.relname as base,a.relkind
from
pg_class a
join pg_depend d on (a.oid = d.refobjid)
join pg_class c on (d.classid = c.oid)
join pg_rewrite r on (objid = r.oid)
join pg_class v on (ev_class = v.oid)
where a.relkind in('r', 'v')
and a.relname <> v.relname
and v.relname='YOUR VIEW NAME HERE'
order by 1
-----Original Message-----
From: pgsql-sql-owner@postgresql.org [mailto:pgsql-sql-owner@postgresql.org]
On Behalf Of Jan Meyland Andersen
Sent: Tuesday, December 26, 2006 3:11 PM
To: Michael Fuhr
Cc: Jan Meyland Andersen; pgsql-sql@postgresql.org
Subject: Re: [SQL] Related tables to a view
> You could query pg_depend to find out which tables and columns the
> view's rewrite rule depends on but that's not as specific as what
> you're requesting. I'm not aware of a way to associate a particular
> table column with a particular view column short of parsing the view
> definition or rule action; doing so would have to allow for the
> possibility of a view column deriving its value from an arbitrarily
> complex expression involving multiple tables, subqueries, etc.
I have been thinking the problem through again, and I think I am able to
solve the problem if I just know which tables the view is using.
But how do I get this information from the pg_depend table?
Regards
Jan
---------------------------(end of broadcast)---------------------------
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> Try this query
>
>
> select a.relname as base,a.relkind
> from
> pg_class a
> join pg_depend d on (a.oid = d.refobjid)
> join pg_class c on (d.classid = c.oid)
> join pg_rewrite r on (objid = r.oid)
> join pg_class v on (ev_class = v.oid)
> where a.relkind in('r', 'v')
> and a.relname <> v.relname
> and v.relname='YOUR VIEW NAME HERE'
> order by 1
>
Thanks a lot. That is exactly what I need.
Regards
Jan