Обсуждение: What is a tuple?
My apologies for the stupid question, but before I started using postgres I never came across the word "tuple" quite in this context before. I know a "tuple" as "a data object containing two or more components" ... but I'm not sure of its precise meaning in the postgres universe. Is a tuple a row, a field value, a field value paired with its datatype, what? If someone asks me the size of my largest tuple, how do I calculate it? It seems to be related deeply to the structure of postgres somehow. Thanks for your patience. Elaine
On Tue, 25 Jun 2002 14:40:03 -0700
Elaine Lindelef <eel@cognitivity.com> wrote:
> My apologies for the stupid question, but before I started using
> postgres I never came across the word "tuple" quite in this context
> before. I know a "tuple" as "a data object containing two or more
> components" ... but I'm not sure of its precise meaning in the
> postgres universe. Is a tuple a row, a field value, a field value
> paired with its datatype, what? If someone asks me the size of my
> largest tuple, how do I calculate it? It seems to be related deeply
> to the structure of postgres somehow.
>
A 'tuple' is not a database - nor PostgreSQL - term. It is a
mathimatical term meaing a set. Withen the context of databases, a tuple
is always a row. 'Tuples' refers to the tuple set, or row set.
On Tue, Jun 25, 2002 at 02:40:03PM -0700, Elaine Lindelef wrote: > My apologies for the stupid question, but before I started using > postgres I never came across the word "tuple" quite in this context > before. I know a "tuple" as "a data object containing two or more > components" ... but I'm not sure of its precise meaning in the > postgres universe. Is a tuple a row, a field value, a field value > paired with its datatype, what? If someone asks me the size of my > largest tuple, how do I calculate it? It seems to be related deeply > to the structure of postgres somehow. A tuple is a row. Isn't this in the glossary somewhere? -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > There are 10 kinds of people in the world, those that can do binary > arithmetic and those that can't.
On Tue, 25 Jun 2002, Timothy Reaves wrote:
> A 'tuple' is not a database - nor PostgreSQL - term. It is a
> mathimatical term meaing a set. Withen the context of databases, a tuple
> is always a row. 'Tuples' refers to the tuple set, or row set.
And, in the same mathematical language of relational databases, what we
commonly call a "table" is a "relation". "Columns" are called "attributes".
A good database management book will teach you the vocabulary.
Rich
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Martijn van Oosterhout wrote: > On Tue, Jun 25, 2002 at 02:40:03PM -0700, Elaine Lindelef wrote: > > My apologies for the stupid question, but before I started using > > postgres I never came across the word "tuple" quite in this context > > before. I know a "tuple" as "a data object containing two or more > > components" ... but I'm not sure of its precise meaning in the > > postgres universe. Is a tuple a row, a field value, a field value > > paired with its datatype, what? If someone asks me the size of my > > largest tuple, how do I calculate it? It seems to be related deeply > > to the structure of postgres somehow. > > A tuple is a row. Isn't this in the glossary somewhere? It's in the FAQ. -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000 + If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania 19026
> > A tuple is a row. Isn't this in the glossary somewhere?
>
>It's in the FAQ.
>
Thank you all for your help. Tuple = Row ; that makes sense.
However, I do want to assure you that I spent some time on the
postgresql.org website trying to find this information:
- What glossary? I really did look hard!
- No, it's not in the (English) FAQ. The only line about tuples is:
"5.3) How do I write a C function to return a tuple?
This requires wizardry so extreme that the authors have never
tried it, though in principle it can be done."
And, since other areas of the FAQ and documentation use "row", it's
easy to suspect that perhaps there's a different meaning for "tuple."
(I presume what really happened is that different writers happened to
prefer different vocabulary.)
Perhaps someone would be kind enough to add this to the FAQ, or make
the glossary more prominent on the site if it is explained there.
Elaine
Elaine Lindelef wrote:
> > > A tuple is a row. Isn't this in the glossary somewhere?
> >
> >It's in the FAQ.
> >
>
> Thank you all for your help. Tuple = Row ; that makes sense.
>
> However, I do want to assure you that I spent some time on the
> postgresql.org website trying to find this information:
>
> - What glossary? I really did look hard!
>
> - No, it's not in the (English) FAQ. The only line about tuples is:
>
> "5.3) How do I write a C function to return a tuple?
> This requires wizardry so extreme that the authors have never
> tried it, though in principle it can be done."
>
> And, since other areas of the FAQ and documentation use "row", it's
> easy to suspect that perhaps there's a different meaning for "tuple."
> (I presume what really happened is that different writers happened to
> prefer different vocabulary.)
>
> Perhaps someone would be kind enough to add this to the FAQ, or make
> the glossary more prominent on the site if it is explained there.
Already in the FAQ:
<H4><A name="4.17">4.17</A>) What is the meaning of some of the
terms used in PostgreSQL?</H4>
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
/usr/local/bin/mime: cannot create /dev/ttyp3: permission denied
this is that i've found in webopedia: tuple=record & record=In database management systems, a complete set of information. i.e. tuple in database management systems = a complete set of information. http://www.webopedia.com/TERM/t/tuple.html --- Bruce Momjian <pgman@candle.pha.pa.us> wrote: > Elaine Lindelef wrote: > > > > A tuple is a row. Isn't this in the glossary > somewhere? > > > > > >It's in the FAQ. > > > > > > > Thank you all for your help. Tuple = Row ; that > makes sense. > > > > However, I do want to assure you that I spent some > time on the > > postgresql.org website trying to find this > information: > > > > - What glossary? I really did look hard! > > > > - No, it's not in the (English) FAQ. The only > line about tuples is: > > > > "5.3) How do I write a C function to return a > tuple? > > This requires wizardry so extreme that the > authors have never > > tried it, though in principle it can be done." > > > > And, since other areas of the FAQ and > documentation use "row", it's > > easy to suspect that perhaps there's a different > meaning for "tuple." > > (I presume what really happened is that different > writers happened to > > prefer different vocabulary.) > > > > Perhaps someone would be kind enough to add this > to the FAQ, or make > > the glossary more prominent on the site if it is > explained there. > > Already in the FAQ: > > <H4><A name="4.17">4.17</A>) What is the meaning > of some of the > terms used in PostgreSQL?</H4> > > -- > Bruce Momjian | > http://candle.pha.pa.us > pgman@candle.pha.pa.us | (610) > 853-3000 > + If your life is a hard drive, | 830 Blythe > Avenue > + Christ can be your backup. | Drexel > Hill, Pennsylvania 19026 > /usr/local/bin/mime: cannot create /dev/ttyp3: > permission denied > > > > ---------------------------(end of > broadcast)--------------------------- > TIP 6: Have you searched our list archives? > > http://archives.postgresql.org > > __________________________________________________ Do You Yahoo!? Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com
Well, maybe just to keep things fun, I'll confuse the heck out of
all you guys.
To be pedantic, "relation" and "tuple" are mathmatical terms used
in relational algebra; "table" and "row" are references to entities
in physical storage.
A relation cannot contain duplicate tuples, but a table can contain
duplicate rows. So let's look at the following:
key | value
--------+---------------------
1 | one
2 | two
2 | two
This can be a table, but not a relation. The relation wouldn't have
that last row in it.
But in fact, it gets more interesting. Tables don't actually
correspond to relations; they correspond to _relvars_, or variables
that hold relations. Given the following table "foo":
SELECT * FROM foo
key | value
--------+---------------------
1 | one
2 | two
DELETE FROM foo WHERE key = 2
SELECT * FROM foo
key | value
--------+---------------------
1 | one
The two relations you see above are obviously not equal. They're
two different relations. When you deleted that row/tuple, you
effectively assigned a new relation to the relvar "foo".
There's more like this, but it can be most effectively appreciated by
reading C. J. Date's book _An Introduction to Database Systems_.
cjs
--
Curt Sampson <cjs@cynic.net> +81 90 7737 2974 http://www.netbsd.org
Don't you know, in this new Dark Age, we're all light. --XTC
On Thu, Jun 27, 2002 at 09:17:22AM -0400, David Siebert wrote: > Tuple = row... Why not just use row? I know what a tuple is but it seems > like a word to impress more than inform. I can think of a few reasons: 1. Databases have been using the term "tuple" for a very long time. Relational algebra talks about tuples exclusively. 2. The definition of a "tuple" is precise (a set of elements). A "row" could be anything (row in array, row on screen). 3. Whats wrong with having multiple words for the same thing anyway? There's also: relation == table resultset == tuples (?) Anyway, have a nice day :) > -----Original Message----- > From: pgsql-general-owner@postgresql.org > [mailto:pgsql-general-owner@postgresql.org]On Behalf Of Martijn van > Oosterhout > Sent: Tuesday, June 25, 2002 10:54 PM > To: Elaine Lindelef > Cc: pgsql-general@postgresql.org > Subject: Re: [GENERAL] What is a tuple? > > > On Tue, Jun 25, 2002 at 02:40:03PM -0700, Elaine Lindelef wrote: > > My apologies for the stupid question, but before I started using > > postgres I never came across the word "tuple" quite in this context > > before. I know a "tuple" as "a data object containing two or more > > components" ... but I'm not sure of its precise meaning in the > > postgres universe. Is a tuple a row, a field value, a field value > > paired with its datatype, what? If someone asks me the size of my > > largest tuple, how do I calculate it? It seems to be related deeply > > to the structure of postgres somehow. > > A tuple is a row. Isn't this in the glossary somewhere? > -- > Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > > There are 10 kinds of people in the world, those that can do binary > > arithmetic and those that can't. > > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org > > -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > There are 10 kinds of people in the world, those that can do binary > arithmetic and those that can't.
Tuple = row... Why not just use row? I know what a tuple is but it seems like a word to impress more than inform. -----Original Message----- From: pgsql-general-owner@postgresql.org [mailto:pgsql-general-owner@postgresql.org]On Behalf Of Martijn van Oosterhout Sent: Tuesday, June 25, 2002 10:54 PM To: Elaine Lindelef Cc: pgsql-general@postgresql.org Subject: Re: [GENERAL] What is a tuple? On Tue, Jun 25, 2002 at 02:40:03PM -0700, Elaine Lindelef wrote: > My apologies for the stupid question, but before I started using > postgres I never came across the word "tuple" quite in this context > before. I know a "tuple" as "a data object containing two or more > components" ... but I'm not sure of its precise meaning in the > postgres universe. Is a tuple a row, a field value, a field value > paired with its datatype, what? If someone asks me the size of my > largest tuple, how do I calculate it? It seems to be related deeply > to the structure of postgres somehow. A tuple is a row. Isn't this in the glossary somewhere? -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > There are 10 kinds of people in the world, those that can do binary > arithmetic and those that can't. ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
well a row is more a visualation word, when you do a select, you get "rows" back... they look like rows... a tuple is actually what it is. not meant to impress, but just what it is. a tuple is defined as "a data object containing two or more components". hope this clears up some confusion. -chris =On Thu, Jun 27, 2002 at 09:17:22AM -0400, =recieved 1.4K bytes from David Siebert containing this: > Tuple = row... Why not just use row? I know what a tuple is but it seems > like a word to impress more than inform. > > -----Original Message----- > From: pgsql-general-owner@postgresql.org > [mailto:pgsql-general-owner@postgresql.org]On Behalf Of Martijn van > Oosterhout > Sent: Tuesday, June 25, 2002 10:54 PM > To: Elaine Lindelef > Cc: pgsql-general@postgresql.org > Subject: Re: [GENERAL] What is a tuple? > > > On Tue, Jun 25, 2002 at 02:40:03PM -0700, Elaine Lindelef wrote: > > My apologies for the stupid question, but before I started using > > postgres I never came across the word "tuple" quite in this context > > before. I know a "tuple" as "a data object containing two or more > > components" ... but I'm not sure of its precise meaning in the > > postgres universe. Is a tuple a row, a field value, a field value > > paired with its datatype, what? If someone asks me the size of my > > largest tuple, how do I calculate it? It seems to be related deeply > > to the structure of postgres somehow. > > A tuple is a row. Isn't this in the glossary somewhere? > -- > Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > > There are 10 kinds of people in the world, those that can do binary > > arithmetic and those that can't. > > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org > > > > > > ---------------------------(end of broadcast)--------------------------- > TIP 4: Don't 'kill -9' the postmaster >
I think tuple comes from a more classical description where tables are relations and is mainly used in the description of relational model concepts. Elmasri and Nevathe (Fundamentals of Database Systems) describe a tuple as a row and don't seem to make any distinction between the two, Date (Introduction to Database Systems) promises as full and formal description of exactly what a tuple is but doesn't deliver it and makes the same equivelence. At Uni we used tuples and the more formal relation language to describe databases but at work we use rows as the language is more easily understood. I do agree with your point that it may be a way to impress more than inform but think it may be just a language thing, with some people preferring one over the other. Steve > -----Original Message----- > From: David Siebert [mailto:dsiebert@eclipsecat.com] > Sent: 27 June 2002 14:17 > To: Martijn van Oosterhout > Cc: pgsql-general@postgresql.org > Subject: Re: [GENERAL] What is a tuple? > > > Tuple = row... Why not just use row? I know what a tuple is > but it seems > like a word to impress more than inform. > > -----Original Message----- > From: pgsql-general-owner@postgresql.org > [mailto:pgsql-general-owner@postgresql.org]On Behalf Of Martijn van > Oosterhout > Sent: Tuesday, June 25, 2002 10:54 PM > To: Elaine Lindelef > Cc: pgsql-general@postgresql.org > Subject: Re: [GENERAL] What is a tuple? > > > On Tue, Jun 25, 2002 at 02:40:03PM -0700, Elaine Lindelef wrote: > > My apologies for the stupid question, but before I started using > > postgres I never came across the word "tuple" quite in this context > > before. I know a "tuple" as "a data object containing two or more > > components" ... but I'm not sure of its precise meaning in the > > postgres universe. Is a tuple a row, a field value, a field value > > paired with its datatype, what? If someone asks me the size of my > > largest tuple, how do I calculate it? It seems to be related deeply > > to the structure of postgres somehow. > > A tuple is a row. Isn't this in the glossary somewhere? > -- > Martijn van Oosterhout <kleptog@svana.org> > http://svana.org/kleptog/ > > There are 10 kinds of people in the world, those that can do binary > > arithmetic and those that can't. > > > > ---------------------------(end of > broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to > majordomo@postgresql.org > > > > > > ---------------------------(end of > broadcast)--------------------------- > TIP 4: Don't 'kill -9' the postmaster > >
Perhaps I've been incorrect but I've normally used 'row' when referring to the tuple that actually exists on disk and returned by a straight SELECT SELECT attr,attr,attr FROM ... I've used tuple when I want to refer to the virtual, only in memory row that is created through things like: SELECT a.attr,b.attr FROM ... a, ... b My point being that when I'm talking about something more abstract to use the more abstract form. It's just sort of a way for me to keep things straight in conversation. Joshua b. Jore ; http://www.greentechnologist.org On Fri, 28 Jun 2002, Chris Humphries wrote: > well a row is more a visualation word, when you do a select, you > get "rows" back... they look like rows... > > a tuple is actually what it is. not meant to impress, but just what > it is. a tuple is defined as "a data object containing two or more > components". > > hope this clears up some confusion. > > -chris > > > =On Thu, Jun 27, 2002 at 09:17:22AM -0400, > =recieved 1.4K bytes from David Siebert containing this: > > Tuple = row... Why not just use row? I know what a tuple is but it seems > > like a word to impress more than inform. > > > > -----Original Message----- > > From: pgsql-general-owner@postgresql.org > > [mailto:pgsql-general-owner@postgresql.org]On Behalf Of Martijn van > > Oosterhout > > Sent: Tuesday, June 25, 2002 10:54 PM > > To: Elaine Lindelef > > Cc: pgsql-general@postgresql.org > > Subject: Re: [GENERAL] What is a tuple? > > > > > > On Tue, Jun 25, 2002 at 02:40:03PM -0700, Elaine Lindelef wrote: > > > My apologies for the stupid question, but before I started using > > > postgres I never came across the word "tuple" quite in this context > > > before. I know a "tuple" as "a data object containing two or more > > > components" ... but I'm not sure of its precise meaning in the > > > postgres universe. Is a tuple a row, a field value, a field value > > > paired with its datatype, what? If someone asks me the size of my > > > largest tuple, how do I calculate it? It seems to be related deeply > > > to the structure of postgres somehow. > > > > A tuple is a row. Isn't this in the glossary somewhere? > > -- > > Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > > > There are 10 kinds of people in the world, those that can do binary > > > arithmetic and those that can't. > > > > > > > > ---------------------------(end of broadcast)--------------------------- > > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org > > > > > > > > > > > > ---------------------------(end of broadcast)--------------------------- > > TIP 4: Don't 'kill -9' the postmaster > > > > > > ---------------------------(end of broadcast)--------------------------- > TIP 2: you can get off all lists at once with the unregister command > (send "unregister YourEmailAddressHere" to majordomo@postgresql.org) > > >
I've always wondered that myself! And this is the answer I came up with in my head: Tuple is an abstract term. You can use it when discussing a set of data. Row is a physical term, referring to a row in a database table. So, when talking about any row in any table (which may or may not be physical), it is appropriate to use the term "tuple". But when speaking of a database in a non-abstract sense, it is better just to say "row". Hope my input helps. :) - Daryl. > -----Original Message----- > From: David Siebert [mailto:dsiebert@eclipsecat.com] > Sent: Thursday, June 27, 2002 9:17 AM > To: Martijn van Oosterhout > Cc: pgsql-general@postgresql.org > Subject: Re: [GENERAL] What is a tuple? > > > Tuple = row... Why not just use row? I know what a tuple is > but it seems > like a word to impress more than inform. > > -----Original Message----- > From: pgsql-general-owner@postgresql.org > [mailto:pgsql-general-owner@postgresql.org]On Behalf Of Martijn van > Oosterhout > Sent: Tuesday, June 25, 2002 10:54 PM > To: Elaine Lindelef > Cc: pgsql-general@postgresql.org > Subject: Re: [GENERAL] What is a tuple? > > > On Tue, Jun 25, 2002 at 02:40:03PM -0700, Elaine Lindelef wrote: > > My apologies for the stupid question, but before I started using > > postgres I never came across the word "tuple" quite in this context > > before. I know a "tuple" as "a data object containing two or more > > components" ... but I'm not sure of its precise meaning in the > > postgres universe. Is a tuple a row, a field value, a field value > > paired with its datatype, what? If someone asks me the size of my > > largest tuple, how do I calculate it? It seems to be related deeply > > to the structure of postgres somehow. > > A tuple is a row. Isn't this in the glossary somewhere? > -- > Martijn van Oosterhout <kleptog@svana.org> > http://svana.org/kleptog/ > > There are 10 kinds of people in the world, those that can do binary > > arithmetic and those that can't. > > > > ---------------------------(end of > broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to > majordomo@postgresql.org > > > > > > ---------------------------(end of > broadcast)--------------------------- > TIP 4: Don't 'kill -9' the postmaster > >