Re: BUG #16462: Update Statement destructive behaviour with joins

On Wed, May 27, 2020 at 12:48:19AM +1200, David Rowley wrote:
> On Wed, 27 May 2020 at 00:15, PG Bug reporting form
> <noreply@postgresql.org> wrote:
> > Let's say I have a table orange and a temp table temp, and i want to update
> > the records after joining the columns in temp table. I used the following
> > syntax to update the records which ended up updating the entire table
> > "orange".
> >
> >        UPDATE orange
> >            SET fruit_flag = 'okay'
> >             FROM temp as t
> >                    INNER JOIN portal_users p on t.fruit_id = p.fruit_id
> >             WHERE p.id = '123';
> >
> > I know that the correct syntax should be the following but judging from the
> > destructive nature of this query i honestly feel we should throw validation
> > error if the above syntax is not correct.
> 
> That's an unfortunate mistake.
> 
> Unfortunately, SQL is full of these trip hazards. The join syntax was
> once revised to try to reduce the pain of accidental cartesian joins
> by missed join clauses in the WHERE clause.  The JOIN ON syntax was
> born because of that. Maybe we didn't get the UPDATE FROM syntax
> perfect, as it does still allow users to easily miss the join clause,
> but I'm not all that sure what we can realistically do about that,  It
> does not seem like a good thing to go raising an error as it might
> block some genuine use case.
> 
> Thinking back, there was some discussion around looking for ways to
> block such mistakes in [1]. As I recall it was going to be an
> extension that created triggers to block mistakes like this.  However,
> that thread has not moved in over 3 years.
> 
> [1] https://www.postgresql.org/message-id/flat/20170202175023.GA30233%40localhost#95ca7fad07b30fd0e2205075f3fc04c5

I have alawys wanted a 'novice' mode which warned/errored on such things.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EnterpriseDB                             https://enterprisedb.com

  The usefulness of a cup is in its emptiness, Bruce Lee