Re: Document NULL

hi.

"SQL specification" should be "SQL standard"?

+ another null vale and unequal to all other values.
typo. should be "another null value"

other places using subsection, many places in doc/src/sgml/nullvalues.sgml
using "sub-section".

+ Notice two important behaviors: first, even though we passed in a
null value to
+ to the <literal>set_config</literal> function, the
<literal>current_setting</literal>
there is two "to to".

gmail has grammar checks, chatgpt can also help find typos.
you can give it a try.

+ <programlisting>
+ BEGIN;
+ ALTER TABLE null_examples ADD CONSTRAINT value_not_1 CHECK (value != 1);
+ ROLLBACK;
+ </programlisting>
+ <screen>
+ BEGIN
+ ERROR: check constraint "value_not_1" of relation
"null_examples" is violated by some row
+ ROLLBACK
+ </screen>
+ <programlisting>
+ BEGIN;
+ ALTER TABLE null_examples ADD CONSTRAINT value_not_10 CHECK (value != 10);
+ ROLLBACK;
+ </programlisting>
+ <screen>
+ BEGIN
+ ALTER TABLE
+ ROLLBACK
+ </screen>

i think this part, BEGIN... ROLLBACK is not necessary.
since if we add these check constraints, it won't influence the
later(next) section.