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Thread: tid scan - is it ever used?

tid scan - is it ever used?

From
"murphy pope"
Date:
I realize this might be "hackers" question, but I was wondering if anyone
has ever seen a "tid scan" in a query plan?

I think a tid scan would only be used if you did something like:

  select ctid from mytable;

are there any other uses for a tid scan?

  -- Thanks, Murphy

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Re: tid scan - is it ever used?

From
Jan Wieck
Date:
murphy pope wrote:
> I realize this might be "hackers" question, but I was wondering if anyone
> has ever seen a "tid scan" in a query plan?
>
> I think a tid scan would only be used if you did something like:
>
>   select ctid from mytable;

    AFAIK  the  tidscan  is used when one specifies "WHERE ctid =
    ...".

> are there any other uses for a tid scan?

    Currently it is the fastest possible access to a single  row.
    So  an application that selects data and wants to update rows
    is optimized for PostgreSQL if it knows about that  fact  and
    qualifies the updates by ctid.

    I thought about getting ctid as a junk attribute when doing a
    SELECT ... FOR UPDATE in a cursor and using that  information
    in UPDATE ... WHERE CURRENT OF <cursorname>.


Jan

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# It's easier to get forgiveness for being wrong than for being right. #
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how to remove columns from a table

From
Fabricio Boppre
Date:
hi,

i am trying to remove a column from a table, but i have not been successful
yet...

can anyone help me?

sorry if it is too simple, but i'm a new user and there was nothing to help me
in the guides i have read.

thanks,
Fabricio

Re: how to remove columns from a table

From
Neil Conway
Date:
On Thu, 6 Jun 2002 15:39:11 -0300
"Fabricio Boppre" <fabricio@gprog.com.br> wrote:
> i am trying to remove a column from a table, but i have not been successful
> yet...

http://www.ca.postgresql.org/docs/faq-english.html#4.4

Cheers,

Neil

--
Neil Conway <neilconway@rogers.com>
PGP Key ID: DB3C29FC

Re: how to remove columns from a table

From
Vivek Khera
Date:
>>>>> "NC" == Neil Conway <nconway@klamath.dyndns.org> writes:

NC> On Thu, 6 Jun 2002 15:39:11 -0300
NC> "Fabricio Boppre" <fabricio@gprog.com.br> wrote:
>> i am trying to remove a column from a table, but i have not been successful
>> yet...

NC> http://www.ca.postgresql.org/docs/faq-english.html#4.4

Which is useless if you have foreign keys referencing your table.

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