2016-12-29 20:23 GMT+01:00 Fabien COELHO <coe...@cri.ensmp.fr>: > > There is a singleton table :) >> >> create table foo(x integer unique not null default 1 check(x = 1), y >> integer); >> insert into foo(y) values(100); >> analyze foo; >> > > I know this one. It can be empty, which a singleton cannot be. For a > singleton table, you should have one and only one row, you cannot insert or > delete, so this is only part of the real thing.
subselect is "singleton" - it returns one row every time. Not sure if term "singleton" is valid in relation database. > > > For example - MySQL @var is volatile - can be changed in query - that's >> mean, you cannot use it as const for planner :( >> > > Indeed, because of the ":=" within in a SELECT query, the variable is > updated at each round. Yuk. > > -- > Fabien. >