On Sun, Dec 26, 2021, at 1:09 PM, Alvaro Herrera wrote:
On 2021-Dec-26, Euler Taveira wrote:
> On Sat, Dec 25, 2021, at 1:20 AM, Amit Kapila wrote:
> > >
> > > So, IMO the PG docs wording for this part should be relaxed a bit.
> > >
> > > e.g.
> > > BEFORE:
> > > + A nullable column in the <literal>WHERE</literal> clause could cause the
> > > + expression to evaluate to false; avoid using columns without not-null
> > > + constraints in the <literal>WHERE</literal> clause.
> > > AFTER:
> > > + A nullable column in the <literal>WHERE</literal> clause could cause the
> > > + expression to evaluate to false. To avoid unexpected results, any possible
> > > + null values should be accounted for.
Is this actually correct? I think a null value would cause the
expression to evaluate to null, not false; the issue is that the filter
considers a null value as not matching (right?). Maybe it's better to
spell that out explicitly; both these wordings seem distracting.
[Reading it again...] I think it is referring to the
pgoutput_row_filter_exec_expr() return. That's not accurate because it is
talking about the expression and the expression returns true, false and null.
However, the referred function returns only true or false. I agree that we
should explictily mention that a null return means the row won't be published.
You have this elsewhere:
+ If the optional <literal>WHERE</literal> clause is specified, only rows
+ that satisfy the <replaceable class="parameter">expression</replaceable>
+ will be published. Note that parentheses are required around the
+ expression. It has no effect on <literal>TRUNCATE</literal> commands.
Maybe this whole thing is clearer if you just say "If the optional WHERE
clause is specified, rows for which the expression returns false or null
will not be published." With that it should be fairly clear what
happens if you have NULL values in the columns used in the expression,
and you can just delete that phrase you're discussing.
Your proposal sounds good to me.