> On Oct 6, 2016, at 5:25 AM, Vitaly Burovoy <vitaly.buro...@gmail.com> wrote: > > On 10/6/16, Simon Riggs <si...@2ndquadrant.com> wrote: >> On 6 October 2016 at 04:43, Serge Rielau <se...@rielau.com> wrote: >>>>> Or should I compose some sort of a design document? >> >> Having read this thread, I'm a little unclear as to what you're >> writing now, though there's definitely good ideas here. >> >> I think it would be beneficial to write up a single coherent >> description of this, including behaviour and a small sketch of >> implementation, just so everyone knows what this is. No design doc, >> but a summary. > > At the moment I think it can also be a good idea to post the current > patch as a Proposal or a WIP to get initial feedback. I can do that - Accompanied by a posting sized overview.
> > Yes, it works for stable "now()" but does not work for volatile > functions like "random()", "uuid_generate_v4()" or default for serial > columns. The only possible way I can see is to check an expression has > only "T_Const"s, static and stable functions. In such case the > expression can be evaluated and the result be saved as a value for > absented attributes of a tuple. In the other case save NULL there and > rewrite the table. Agreed. I think DEFAULT as-is does the job nicely function wise. One can always decompose the ADD COLUMN into two steps within the same transaction if the initial column value for pre-existing rows does not match the default for new or updated rows. AT Just needs a performance boost for large tables where that’s reasonably possible. >> Which makes me think we should call this missing_value or absent_value >> so its clear that it is not a "default" it is the value we use for >> rows that do not have any value stored for them. > > It is definitely a default for a user, it is not a regular default internally. > I'm not a native speaker, "absent_value" can be mixed up with a NULL. > As for me the best phrase is "pre-add-column-default", but it is > impossible to use it as a column name. :-( > It is still an open question. I like Tom’s “creation default”. Another one could be “initial default”. But that, too, can be misread. Cheers Serge Rielau Salesforce.com -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers