PG7.1.2 on RH7.0
select 'a'<>null; ?column? ---------- (1 row)
select 'a'!=null; ?column? ---------- (1 row)
select 'a'=null; ?column? ---------- f(1 row)
select 'a'||null; ?column? ---------- (1 row)
Can someone please explain the above?