From: | Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> |
---|---|
To: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> |
Cc: | Craig Ringer <craig(at)2ndquadrant(dot)com>, Fabrízio de Royes Mello <fabriziomello(at)gmail(dot)com>, Joe Conway <mail(at)joeconway(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: proposal: session server side variables |
Date: | 2016-12-29 19:51:01 |
Message-ID: | CAFj8pRDe62_xfTkKkM5q7qeGWrrxD_Jck2QTxjLvMO8_2qaUOQ@mail.gmail.com |
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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.
>
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