Re: Check constraints do not seem to be working!!!

On 11/11/20 10:06 AM, Jitendra Loyal wrote:
> Thanks Nikolay
>
> I read that but is there a way to meet the above requirement. And I will
> like to add that IS NULL and IS NOT NULL should evaluate to true/false.
> These operators are made for this and should not be returning NULL.
>

This has nothing to do with IS [NOT] NULL, it's the first part of the
expression (b = TRUE) causing trouble. Essentially, the constraint

(b = true) and (c is not null)

is evaluated in two steps. First we evaluate the two parts individually,
and for (null, true) the results would look like this:

(b = true) => null
(c is not null) => true

and then we combine those results using 'AND'

null AND true => null

which is considered as if the constraint matches. If you want to handle
NULL for the first expression, you may do this, for example:

(b it not null and b = true) and (c is not null)

Or something like that.

regards

--
Tomas Vondra
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