Thread

1. RE: [HACKERS] Recursive queries?

   Michael Meskes <meskes@topsystem.de> — 1998-02-20T10:35:18Z

   But such a statement is executed only once, isn't it?
   
   Postquel did execute a retrieve* into as long as it was able to generate
   new data.
   
   Michael
   
   P.S.: Glad I'm not the only one interested in this. :-)
   
   --
   Dr. Michael Meskes, Project-Manager    | topsystem Systemhaus GmbH
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   > -----Original Message-----
   > From:	Vadim B. Mikheev [SMTP:vadim@sable.krasnoyarsk.su]
   > Sent:	Friday, February 20, 1998 10:59 AM
   > To:	Michael Meskes
   > Cc:	PostgreSQL Hacker
   > Subject:	Re: [HACKERS] Recursive queries?
   > 
   > Michael Meskes wrote:
   > > 
   > > I know that postgres originally was able to do recursive queries
   > like
   > > 
   > > retrieve* into a from a ...
   > > 
   > > Is this still possible with PostgreSQL? If so, is it just for one
   > statement
   > > or even as a block?
   > 
   > Yes, it's possible. This is from spi.txt:
   > ---
   >                          Data changes visibility
   > 
   >    PostgreSQL data changes visibility rule: during a query execution,
   > data
   > changes made by the query itself (via SQL-function, SPI-function,
   > triggers)
   > are invisible to the query scan.  For example, in query
   > 
   >    INSERT INTO a SELECT * FROM a
   > 
   >    tuples inserted are invisible for SELECT' scan.  In effect, this
   > duplicates the database table within itself (subject to unique index
   > rules, of course) without recursing.
   > 
   >    Changes made by query Q are visible by queries which are started
   > after
   > query Q, no matter whether they are started inside Q (during the
   > execution
   > of Q) or after Q is done.
   > ---
   > 
   > Second query 'INSERT INTO a SELECT * FROM a' inside BEGIN/END
   > will see tuples inserted by first one. Pg uses special CommandCounter
   > to distinguish changes made in the same transaction.
   > 
   > > This happens to be the area I worked on for several years.
   > 
   > I also like such areas :)
   > 
   > Vadim
   
   

2. Re: [HACKERS] Recursive queries?

   Thomas Lockhart <lockhart@alumni.caltech.edu> — 1998-02-20T16:44:15Z

   > But such a statement is executed only once, isn't it?
   >
   > Postquel did execute a retrieve* into as long as it was able to generate
   > new data.
   
   OK, I'll bite :)
   Can you give an example of this? How does new data become available in the
   middle of a transaction? Just curious...