Thanks for the response. Really appreciate it! Regards, Ivy
2018-08-20 10:40 GMT-07:00 David G. Johnston <david.g.johns...@gmail.com>: > On Monday, August 20, 2018, Wu Ivy <ivywu...@gmail.com> wrote: >> >> Thanks for the quick respond. >> Why are SELECT query never marked nullable? For nullable columns, when I >> call SPI_getvalue(), the result (in char*) is NULL. I don’t think I’m too >> clear on the definition of *attnotnull*. Can you give me a example in >> which the tupleTable is can be marked nullable? >> Also, is there any other ways to get nullability of each column while >> getting the data from SPI_cursor_fetch? The only way I can think is to call >> another separate command to query the table schema, but it will be in a >> separate transaction in that case. >> > > Basically the nullability property is used by the planner for optimization > during the joining of physical tables. As soon as you try outputting > columns the ability to enforce not null goes away because of, in > particular, outer joins. While some changes could maybe be made the > cost-benefit to do so doesn't seem favorable. > > David J. > >
