good table design...

[toedipper]

Hello,

I am designing a table of vehicle types, nothing special, just a list of
unique vehicle types such as truck, lorry, bike, motor bike, plane, tractor
etc etc

For the table design I am proposing a single column table with a field name
called vehicle_type and this will contain the vehicle type.

Sot it will be

vehicle_type
car
bike
tractor
plane
truck
van
blah
blah
blah

Is this ok? Or is there a better way to do it?

Thanks,

td.

[--CELKO--]

Re: good table design...

>> For the table design I am proposing a single column table with a
field [sic] name called vehicle_type and this will contain the vehicle
type... Is this ok? <<

Sure, if you remember to make the one column the primary key. It is
weird just hanging out there in space without anything in the schema,
but it is legal. And fields are not anything like column.

[toedipper]

Re: good table design...

Thanks for your reply.

Totally of topic but what does 'sic' mean? I see this all over the place
both on the web and in print.

Thanks,

TD.


"--CELKO--" <jcelko212@eart hlink.net> wrote in message
news:18c7b3c2.0 411251010.13393 2be@posting.goo gle.com...[color=blue][color=green][color=darkred]
> >> For the table design I am proposing a single column table with a[/color][/color]
> field [sic] name called vehicle_type and this will contain the vehicle
> type... Is this ok? <<
>
> Sure, if you remember to make the one column the primary key. It is
> weird just hanging out there in space without anything in the schema,
> but it is legal. And fields are not anything like column.[/color]

[David Portas]

Re: good table design...

Best way to describe a table is as DDL:

CREATE TABLE Vehicles (vehicle_type VARCHAR(20) PRIMARY KEY)

Nothing wrong with this on its own but you need to consider its place in the
schema as a whole rather than in isolation. Vehicle_type may not necessarily
be appropriate or convenient as a foreign key in other tables.

--
David Portas
SQL Server MVP
--

[David Portas]

Re: good table design...

I recommend you invest in a dictionary... or Google for one :-)

In SQL we have columns and rows NOT fields and records. Conceptually they
are quite different.

--
David Portas
SQL Server MVP
--

[Hilarion]

Re: good table design...

> In SQL we have columns and rows NOT fields and records. Conceptually they are quite different.

Could you point the differences, please?
I could swear that in relational DB terminology fields and records are
common. SQL DBs are relational DBs.

Hilarion

[David Portas]

Re: good table design...

> Could you point the differences, please?

http://www.google.com/groups?selm=e%24kTfz2jDHA.1728%40TK2MSFTNGP11.phx.gbl&rnum=6

[color=blue]
> SQL DBs are relational DBs.[/color]
I'll watch out for that one to be quoted on www.dbdebunk.com ;-)

--
David Portas
SQL Server MVP
--

[Joe Celko]

Re: good table design...

why do you kids know all the internet codes and emoticons, but not
Latin? "sic" means "error in the original"; look up etc., et al, ibid,
e.g., i.e. and so forth.

Better yet, look up the telegram codes.

--CELKO--
Please post DDL, so that people do not have to guess what the keys,
constraints, Declarative Referential Integrity, datatypes, etc. in your
schema are. Sample data is also a good idea, along with clear
specifications.


*** Sent via Developersdex http://www.developersdex.com ***
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[Erland Sommarskog]

Re: good table design...

toedipper (send_rubbish_h ere734@hotmail. com) writes:[color=blue]
> I am designing a table of vehicle types, nothing special, just a list of
> unique vehicle types such as truck, lorry, bike, motor bike, plane,
> tractor
>
> For the table design I am proposing a single column table with a field
> name called vehicle_type and this will contain the vehicle type.[/color]

Normally you would use this value somewhere. In that case it's usually
a bit akward to have the string "tractor" all over the place. So rather
you would have things like:

CREATE TABLE vehicle_types (vtypid smallint NOT NULL,
vtypname varchar(20) NOT NULL,
CONSTRAINT pk_vtype PRIMARY KEY (vtypid))

CREATE TABLE vehicles (vehicleid int NOT NULL,
...
vehicle_type smallint NOT NULL,
...
CONSTRAINT fk_vehicle_type FOREIGN KEY (vehicle_type)
REFERNENCES vehicle_types (vtypid))

If your code includes hard coded tests for various vehicle types, a short
char field for a mnemonic code may be better.
--
Erland Sommarskog, SQL Server MVP, esquel@sommarsk og.se

Books Online for SQL Server SP3 at

http://www.microsoft.com/sql/techinfo/productdoc/2000/books.asp

[Joe Celko]

Re: good table design...

Like most new ideas, the hard part of understanding what the relational
model is comes in un-learning what you know about file systems.

As Artemus Ward (William Graham Sumner, 1840-1910) put it, "It ain't so
much the things we don't know that get us into trouble. It's the things
we know that just ain't so."

If you already have a background in data processing with traditional
file systems, the first things to un-learn are:

(0) Databases are not file sets.
(1) Tables are not files.
(2) Rows are not records.
(3) Columns are not fields.

Modern data processing began with punch cards, or Hollerith cards used
by the Bureau of the Census. Their original size was that of a United
States Dollar bill. This was set by their inventor, Herman Hollerith,
because he could get furniture to store the cards from the United States
Treasury Department, just across the street. Likewise, physical
constraints limited each card to 80 columns of holes in which to record
a symbol.

The influence of the punch card lingered on long after the invention of
magnetic tapes and disk for data storage. This is why early video
display terminals were 80 columns across. Even today, files which were
migrated from cards to magnetic tape files or disk storage still use 80
column records.

But the influence was not just on the physical side of data processing.
The methods for handling data from the prior media were imitated in the
new media.

Data processing first consisted of sorting and merging decks of punch
cards (later, sequential magnetic tape files) in a series of distinct
steps. The result of each step feed into the next step in the process.

Relational databases do not work that way. Each user connects to the
entire database all at once, not to one file at time in a sequence of
steps. The users might not all have the same database access rights
once they are connected, however. Magnetic tapes could not be shared
among users at the same time, but shared data is the point of a
database.

Tables versus Files

A file is closely related to its physical storage media. A table may or
may not be a physical file. DB2 from IBM uses one file per table,
while Sybase puts several entire databases inside one file. A table is
a <i>set<i> of rows of the same kind of thing. A set has no ordering
and it makes no sense to ask for the first or last row.

A deck of punch cards is sequential, and so are magnetic tape files.
Therefore, a <i>physical<i > file of ordered sequential records also
became the <i>mental<i> model for data processing and it is still hard
to shake. Anytime you look at data, it is in some physical ordering.

The various access methods for disk storage system came later, but even
these access methods could not shake the mental model.

Another conceptual difference is that a file is usually data that deals
with a whole business process. A file has to have enough data in
itself to support applications for that business process. Files tend to
be "mixed" data which can be described by the name of the business
process, such as "The Payroll file" or something like that.

Tables can be either entities or relationships within a business
process. This means that the data which was held in one file is often
put into several tables. Tables tend to be "pure" data which can be
described by single words. The payroll would now have separate tables
for timecards, employees, projects and so forth.

Tables as Entities

An entity is physical or conceptual "thing" which has meaning be itself.
A person, a sale or a product would be an example. In a relational
database, an entity is defined by its attributes, which are shown as
values in columns in rows in a table.

To remind users that tables are sets of entities, I like to use plural
or collective nouns that describe the function of the entities within
the system for the names of tables. Thus "Employee" is a bad name
because it is singular; "Employees" is a better name because it is
plural; "Personnel" is best because it is collective and does not summon
up a mental picture of individual persons.

If you have tables with exactly the same structure, then they are sets
of the same kind of elements. But you should have only one set for each
kind of data element! Files, on the other hand, were PHYSICALLY
separate units of storage which could be alike -- each tape or disk file
represents a step in the PROCEDURE , such as moving from raw data, to
edited data, and finally to archived data.

Tables as Relationships

A relationship is shown in a table by columns which reference one or
more entity tables. Without the entities, the relationship has no
meaning, but the relationship can have attributes of its own. For
example, a show business contract might have an agent, an employer and a
talent. The method of payment is an attribute of the contract itself,
and not of any of the three parties.

Rows versus Records

Rows are not records. A record is defined in the application program
which reads it; a row is defined in the database schema and not by a
program at all. The name of the field in the READ or INPUT statements
of the application; a row is named in the database schema.

All empty files look alike; they are a directory entry in the operating
system with a name and a length of zero bytes of storage. Empty tables
still have columns, constraints, security privileges and other
structures, even tho they have no rows.

This is in keeping with the set theoretical model, in which the empty
set is a perfectly good set. The difference between SQL's set model and
standard mathematical set theory is that set theory has only one empty
set, but in SQL each table has a different structure, so they cannot be
used in places where non-empty versions of themselves could not be used.

Another characteristic of rows in a table is that they are all alike in
structure and they are all the "same kind of thing" in the model. In a
file system, records can vary in size, datatypes and structure by having
flags in the data stream that tell the program reading the data how to
interpret it. The most common examples are Pascal's variant record, C's
struct syntax and Cobol's OCCURS clause.

The OCCURS keyword in Cobol and the Variant records in Pascal have a
number which tells the program how many time a record structure is to be
repeated in the current record.

Unions in 'C' are not variant records, but variant mappings for the same
physical memory. For example:

union x {int ival; char j[4];} myStuff;

defines myStuff to be either an integer (which are 4 bytes on most
modern C compilers, but this code is non-portable) or an array of 4
bytes, depending on whether you say myStuff.ival or myStuff.j[0];

But even more than that, files often contained records which were
summaries of subsets of the other records -- so called control break
reports. There is no requirement that the records in a file be related
in any way -- they are literally a stream of binary data whose meaning
is assigned by the program reading them.

Columns versus Fields

A field within a record is defined by the application program that reads
it. A column in a row in a table is defined by the database schema.
The datatypes in a column are always scalar.

The order of the application program variables in the READ or INPUT
statements is important because the values are read into the program
variables in that order. In SQL, columns are referenced only by their
names. Yes, there are shorthands like the SELECT * clause and INSERT
INTO <table name> statements which expand into a list of column names in
the physical order in which the column names appear within their table
declaration, but these are shorthands which resolve to named lists.

The use of NULLs in SQL is also unique to the language. Fields do not
support a missing data marker as part of the field, record or file
itself. Nor do fields have constraints which can be added to them in
the record, like the DEFAULT and CHECK() clauses in SQL.

Relationships among tables within a database

Files are pretty passive creatures and will take whatever an application
program throws at them without much objection. Files are also
independent of each other simply because they are connected to one
application program at a time and therefore have no idea what other
files looks like.

A database actively seeks to maintain the correctness of all its data.
The methods used are triggers, constraints and declarative referential
integrity.

Declarative referential integrity (DRI) says, in effect, that data in
one table has a particular relationship with data in a second (possibly
the same) table. It is also possible to have the database change itself
via referential actions associated with the DRI.

For example, a business rule might be that we do not sell products which
are not in inventory. This rule would be enforce by a REFERENCES clause
on the Orders table which references the Inventory table and a
referential action of ON DELETE CASCADE

Triggers are a more general way of doing much the same thing as DRI. A
trigger is a block of procedural code which is executed before, after or
instead of an INSERT INTO or UPDATE statement. You can do anything with
a trigger that you can do with DRI and more.

However, there are problems with TRIGGERs. While there is a standard
syntax for them in the SQL-92 standard, most vendors have not
implemented it. What they have is very proprietary syntax instead.
Secondly, a trigger cannot pass information to the optimizer like DRI.
In the example in this section, I know that for every product number in
the Orders table, I have that same product number in the Inventory
table. The optimizer can use that information in setting up EXISTS()
predicates and JOINs in the queries. There is no reasonable way to
parse procedural trigger code to determine this relationship.

The CREATE ASSERTION statement in SQL-92 will allow the database to
enforce conditions on the entire database as a whole. An ASSERTION is
not like a CHECK() clause, but the difference is subtle. A CHECK()
clause is executed when there are rows in the table to which it is
attached. If the table is empty then all CHECK() clauses are
effectively TRUE. Thus, if we wanted to be sure that the Inventory
table is never empty, and we wrote:

CREATE TABLE Inventory
( ...
CONSTRAINT inventory_not_e mpty
CHECK ((SELECT COUNT(*) FROM Inventory) > 0), ... );

it would not work. However, we could write:

CREATE ASSERTION Inventory_not_e mpty
CHECK ((SELECT COUNT(*) FROM Inventory) > 0);

and we would get the desired results. The assertion is checked at the
schema level and not at the table level.

--CELKO--
Please post DDL, so that people do not have to guess what the keys,
constraints, Declarative Referential Integrity, datatypes, etc. in your
schema are. Sample data is also a good idea, along with clear
specifications.


*** Sent via Developersdex http://www.developersdex.com ***
Don't just participate in USENET...get rewarded for it!

[Daven Thrice]

Re: good table design...


"toedipper" <send_rubbish_h ere734@hotmail. com> wrote in message
news:30mv0cF30j bh8U1@uni-berlin.de...[color=blue]
> Thanks for your reply.
>
> Totally of topic but what does 'sic' mean? I see this all over the place
> both on the web and in print.[/color]

It means that what was written was written that way intentionally. For
example, one might say that they when they write, they mispel a lot of words
[sic].

There's a pretty good dictionary at http://m-w.com

Also, if you go to google and search for any word, you'll see that word in
the upper-right quadrant of the screen, next to a link that says
[definition]. Click that link and you'll get the definition.

[Lyle Fairfield]

Re: good table design...

Joe Celko <jcelko212@eart hlink.net> wrote in news:41a65261$0 $14485
$c397aba@news.n ewsgroups.ws:
[color=blue]
> why do you kids know all the internet codes and emoticons, but not
> Latin? "sic" means "error in the original" [Sic].[/color]

[Hilarion]

Re: good table design...

>> Could you point the differences, please?[color=blue]
>
> http://www.google.com/groups?selm=e%...phx.gbl&rnum=6[/color]

This post uses terms "records" and "fields" as filesystem terms
(portions of bytes stored in files) and as programming language
structures (eg. unions and structs in C/C++).
I use those terms for logical structures desciption, not only
physical representation. For me a struct in C/C++ is a way to
represent/implement logical record, just as it can implement
table row (it may be not a very good idea).

I agree with the reply to that post:

http://www.google.com/groups?hl=pl&lr=&selm=%23%23LdgL3jDHA.372%40TK2MSFTNGP11.phx.gbl

It's only a matter of treating terms in logical or physical
manner. I can think of terms "column" and "row" in prysical
manner too (eg. for C/C++/Pascal tables or other more or less
complex programming language structures).

The main idea of relational databases is to have relations
between informations. Storing the informations in one
record of one table is one way to represent the relation,
the other one is to use FOREIGN KEYs. It's not that important
if we call smallest part of information a "field" or "column"
or "cell" (the last one is for me the best one in terms of
"columns" and "rows" and very close to "field" term) as long
as we know what we are describing and are able to understand
what another person is trying to describe.
For me much better term than "table" is "set", cause table
suggests sequence of information.

Hilarion

[-P-]

Re: good table design...

"toedipper" <send_rubbish_h ere734@hotmail. com> wrote in message news:30mdqgF31v 3mtU1@uni-berlin.de...[color=blue]
> Hello,
>
> I am designing a table of vehicle types, nothing special, just a list of
> unique vehicle types such as truck, lorry, bike, motor bike, plane, tractor
> etc etc
>
> For the table design I am proposing a single column table with a field name
> called vehicle_type and this will contain the vehicle type.
>
> Sot it will be
>
> vehicle_type
> car
> bike
> tractor
> plane
> truck
> van
> blah
> blah
> blah
>
> Is this ok? Or is there a better way to do it?
>
> Thanks,
>
> td.
>[/color]


I've never liked using the "descriptiv e name" of the entity as its primary key. What happens if that descriptive name
changes, and the table is referenced as a foreign key by other tables? You've got a referential integrity problem
(unless you endorse the use of ON UPDATE CASCADE, which I personally abhor.)

This is where I would use a separate identifier as the primary key. Something that will never change (an
autoincremented integer, for example), so that the "descriptio n" column can contain the more volatile descriptive text.

--
Paul Horan
Sr. Architect
VCI Springfield, Mass

https://www.vcisolutions.com

[Greg D. Moore \(Strider\)]

Re: good table design...


"-P-" <ent_must_die@h otmail.DOTcom> wrote in message
news:fqadnXa8Od VOczrcRVn-iw@adelphia.com ...
[color=blue]
> This is where I would use a separate identifier as the primary key.[/color]
Something that will never change (an[color=blue]
> autoincremented integer, for example), so that the "descriptio n" column[/color]
can contain the more volatile descriptive text.[color=blue]
>[/color]

You realize an autoincremented integer, at least in MS SQL Server is
terrible for this. You can't guarantee that you won't have gaps and you
can't even guarantee that the numbers will remain the same. DBCC CHECKIDENT
can reset things on you, copying them to another DB may completely change
the numbers, etc.

You are right that the descriptions may change. I'd recommend something
like a partial VIN since that's described by an outside authority and pretty
much won't change.

[color=blue]
> --
> Paul Horan
> Sr. Architect
> VCI Springfield, Mass
> www.vcisolutions.com
>
>
>[/color]