On Sun, Oct 02, 2005 at 03:57:37PM +0300, Hannu Krosing wrote: > On P, 2005-10-02 at 01:24 -0400, Greg Stark wrote: > > Of course that only works if the reason they want to set fill the rows with > > the default value isn't precisely because NULL is a perfectly reasonable > > thing > > for the column to have (but not what they want for the existing rows). > > Sure. > > What would be needed for adding new colums with default filling would be > some end-of-tuple marker or stored column count or tuple version nr, and > then a rule (or just default behaviour) of showing default value for > *missing* columns (colno > nr of stored columns).
Actually, PostgreSQL does know the number of columns in a tuple. It would be possible get change heap_getattr to return the default value. However, from a semantic point of view, it would be a bit strange. If you added a column, updated some rows then set a default, that default might end up applying to every row, except the ones you already modified. With careful coding you may be able to get around this. However, a good argument can be made that setting the DEFAULT for a column shouldn't change data anywhere. What about if I want to change the default for new values but not for old ones. That wouldn't work if the database starts adding values randomly, depending on when they are read... Have a nice day, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
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