On 2020-05-22 12:40, Vik Fearing wrote:
If you specify null, then the cycle check expression will always fail,
so it will abort after the first row.  (We should perhaps prohibit
specifying null, but see below.)

I would rather make the cycle check expression work with null.

It works correctly AFAICT.  What is your expectation?

This is something we need to think about.  If we want to check at parse
time whether the two values are not the same (and perhaps not null),
then we either need to restrict the generality of what we can specify,
or we need to be prepared to do full expression evaluation in the
parser.  A simple and practical way might be to only allow string and
boolean literal.  I don't have a strong opinion here.

I'm with Pavel on this one.  Why does it have to be a parse-time error?
  Also, I regularly see people write functions as sort of pauper's
variables, but a function call isn't allowed here.

If not parse-time error, at what time do you want to check it?

As an improvement over the spec, I think the vast majority of people
will be using simple true/false values.  Can we make that optional?

     CYCLE f, t SET is_cycle USING path

would be the same as

     CYCLE f, t SET is_cycle TO true DEFAULT false USING path

I was also considering that.  It would be an easy change to make.

(Apparently, in DB2 you can omit the USING path clause. Not sure how to make that work, however.)

Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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