From: Michael A Nachbaur <mike@nachbaur.com>
To: pgsql-sql@postgresql.org
Subject: Need help creating a BEFORE DELETE trigger
Date: Mon, 30 Jun 2003 14:45:06 -0700
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Hello everyone,

I'm creating two database tables that will be used to cache the results of a 
search.  Basically, when a search is initiated, an entry will be created in 
the "Search" table that represents the search, and a single entry will be 
created in a child table "SearchResults" for every result returned.  A 
foreign key relationship will be associated between the two.

CREATE TABLE Search
( id         SERIAL
, accountid  INTEGER REFERENCES account(id) ON DELETE CASCADE NOT NULL
, sessionnum CHAR(32) UNIQUE NOT NULL
, created    TIMESTAMP DEFAULT CURRENT_TIMESTAMP NOT NULL
, sqlcode    TEXT
);

CREATE TABLE SearchResults_Customer
( id            SERIAL
, searchid      INTEGER REFERENCES search(id) ON DELETE CASCADE NOT NULL
, customerid    INTEGER REFERENCES customer(id) ON DELETE CASCADE
-- All the results go in fields here
);

Now, when any record is deleted in the SearchResults table (via an ON DELETE 
CASCADE, or other trigger), I'd like the entire search set to be deleted 
since the search is now invalid.  Therefore, if a single record in the 
SearchResults table is deleted, I want it to instead delete the associated 
record in the Search table; this'll cause a CASCADE into the SearchResults 
table, toasting my entire result set.

The problem I'm looking at is: could this cause a recursion problem, where the 
cascading deletion will try to cause the whole thing to cascade again?  How 
can I set this up so I can kill an entire tree of data if any one of it's 
members dies?

Thanks in advance.

-- 
/* Michael A. Nachbaur <mike@nachbaur.com>
 * http://nachbaur.com/pgpkey.asc
 */

"I don't know, " said the voice on the PA, "apathetic 
bloody planet, I've no sympathy at all. "