Re: proposal: session server side variables

2016-12-29 20:23 GMT+01:00 Fabien COELHO <coelho(at)cri(dot)ensmp(dot)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.
>