Re: Database design question

sreedhardasi_at_gmail.com wrote:
> I have a database design questions. How can we specify one of two
> columns in a table should be not null? In other words, if one
> column is null then another column should not be null.

In general, you should be able to use a CHECK constraint, something like this:

CREATE TABLE foo (

    bar INTEGER,
    baz INTEGER,
    CHECK (

        (CASE WHEN bar IS NULL THEN 0 ELSE 1 END) +
        (CASE WHEN baz IS NULL THEN 0 ELSE 1 END) 
        = 1

I can't really speak to the particular design, and very likely somebody will take me to task for failure to scream about how NULLs don't belong in any design. ;)

Cheers,
D

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