Thread

Recursive queries?

Michael Meskes <meskes@topsystem.de> — 1998-02-20T09:14:35Z

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?

This happens to be the area I worked on for several years.

Michael
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Re: [HACKERS] Recursive queries?

Vadim Mikheev <vadim@sable.krasnoyarsk.su> — 1998-02-20T09:59:17Z

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