Applied. ---------------------------------------------------------------------------
Bruce Momjian wrote: > Pilling, Michael wrote: > > Hi Kevin, > > > > Thanks for that. Point entirely taken. I think what I would add would > > be in the table 9-1 of operators, an extra column filled in only for > > =, <> and != saying Important: see difference from IS [NOT] NULL. > > Perhaps one reason I didn't pick up on this subtle issue is that IS > > NULL and IS NOT NULL are not listed in this table but they are > > comparison operators, just textual rather than symbolic ones in the > > grammar so they should be in the table. I recall specifically looking > > up what is the not equal operator in this language and only going > > forward from the table, not realising I had to read any further. > > > > I'd also add after "Do not write expression = NULL because NULL is not > > "equal to" NULL." Do not write expression != NULL or <> NULL because > > NULL is not "not equal to" NULL. because while implied, it's not > > obvious that because = doesn't work with NULL that != doesn't either. > > I have written the attached patch to mention <> NULL also returns NULL. > > -- > Bruce Momjian <br...@momjian.us> http://momjian.us > EnterpriseDB http://enterprisedb.com > > + It's impossible for everything to be true. + [ text/x-diff is unsupported, treating like TEXT/PLAIN ] > diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml > new file mode 100644 > index be92e6a..ddfb29a > *** a/doc/src/sgml/func.sgml > --- b/doc/src/sgml/func.sgml > *************** > *** 364,371 **** > </indexterm> > Ordinary comparison operators yield null (signifying <quote>unknown</>), > not true or false, when either input is null. For example, > ! <literal>7 = NULL</> yields null. When this behavior is not suitable, > ! use the > <literal>IS <optional> NOT </> DISTINCT FROM</literal> constructs: > <synopsis> > <replaceable>expression</replaceable> IS DISTINCT FROM > <replaceable>expression</replaceable> > --- 364,371 ---- > </indexterm> > Ordinary comparison operators yield null (signifying <quote>unknown</>), > not true or false, when either input is null. For example, > ! <literal>7 = NULL</> yields null, as does <literal>7 <> NULL</>. > When > ! this behavior is not suitable, use the > <literal>IS <optional> NOT </> DISTINCT FROM</literal> constructs: > <synopsis> > <replaceable>expression</replaceable> IS DISTINCT FROM > <replaceable>expression</replaceable> > > -- > Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-bugs -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-bugs
