Hi all,
So I've been reading the newsgroups, and reading a few books trying to learn
SQL and SQL Server 2000. The books tell me I need a Primary Key, and that
every table should have one. I know (I think) that a Primary Key is a
special field that uniquely identifies each record or row within a table.
My question is this: If I have a field or column whose values are all (and
will be) different in every row, is that what a Primary Key is, or is it not
a primary key until I designate it as such with either a statement or by
right-clicking a little key on the table diagram.
If so, then what is the reason _behind_ why I have to do that, and have a
primary key?
I've been playing with a few tables, and I can select information just fine,
relate tables together with joins, and everything works fine (so far) all
without my designating any Primary Keys--so why, exactly, do I need one, and
exactly what is it?
I would appreciate any help and clarification.
Thanks. 4 1792
Replied in microsoft.publi c.sqlserver.pro gramming.
Please don't multi-post.
--
David Portas
SQL Server MVP
--
David Portas scratched out in the sand Replied in microsoft.publi c.sqlserver.pro gramming.
Please don't multi-post.
....and for those of us who don't subscribe to m.p.s.p, your answer, David,
was...?
--
kai - kai at 3gproductions dot com www.gamephreakz.com || www.filesite.org
"friends don't let friends use windows xp"
Hi Mavis,
As you suggest, a Primary key is a constraint on the column requiring that
every value is (and will be) different
in every row. Furthermore, it requires that no row can have a NULL value for
that column. So those are the restrictions
on a Primary Key field, that it be non-null and that each value be unique.
Further, a Primary Key can be made up of more than
one column. So, each table can have only one Primary Key, but it can be
made up of several columns. (jeesh- so far I'm probably
just making this MORE confusing).
So, although those are the characteristics of a Primary Key, a column is not
one until you designate it as such. The reason behind it is
twofold (there may be more reasons, but only two come to mind at the
moment - Note to self: more coffee):
1. Performance - when you designate a column as a Primary Key, it is
(clustered) indexed to assist in data retrieval.
2. Data Integrity - the database will ensure that every value that is
inserted (or updated) in the table will meet the requirements of a
Primary Key (i.e. unique and non-null) so you don't have to write those
checks into application code.
It's assumed that the Primary Key field will typically be the field used in
table joins, so because it's indexed (it's also a good general plan
to index the foreign key field) your queries will perform better.
I hope this is of some help Mavis,
Steve
"Mavis Tilden" <ma*********@ho tmail.com> wrote in message
news:XV******** ***********@new s20.bellglobal. com... Hi all,
So I've been reading the newsgroups, and reading a few books trying to
learn SQL and SQL Server 2000. The books tell me I need a Primary Key, and that every table should have one. I know (I think) that a Primary Key is a special field that uniquely identifies each record or row within a table.
My question is this: If I have a field or column whose values are all (and will be) different in every row, is that what a Primary Key is, or is it
not a primary key until I designate it as such with either a statement or by right-clicking a little key on the table diagram.
If so, then what is the reason _behind_ why I have to do that, and have a primary key?
I've been playing with a few tables, and I can select information just
fine, relate tables together with joins, and everything works fine (so far) all without my designating any Primary Keys--so why, exactly, do I need one,
and exactly what is it?
I would appreciate any help and clarification.
Thanks.
On Mon, 11 Oct 2004 04:50:11 -0700, filesiteguy wrote: David Portas scratched out in the sand
Replied in microsoft.publi c.sqlserver.pro gramming.
Please don't multi-post.
...and for those of us who don't subscribe to m.p.s.p, your answer, David, was...?
Hi filesiteguy, http://www.google.com/groups?hl=en&l...bellglobal.com
Best, Hugo
--
(Remove _NO_ and _SPAM_ to get my e-mail address) This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
by: js |
last post by:
I am trying to create a primary key constraint on a view in the
following statement. However, I got an error ORA-00907: missing right
parenthesis. If the CONSTRAINT clause is removed, then the view is
created fine. Does anyone know how to creat Primary Key Constraint
for a View? Thanks.
CREATE OR REPLACE VIEW RPT_VW_WMN (
CARD, EC_D_CODE, EC_M_CODE,
START_DATE, PR_NAME, PR_ID, ELIG, ANNUALY, MONTHLY, PENDING,
/* ORA-00907: missing...
|
by: Peter Scott |
last post by:
I created a table that has a column in that needs to contain a full
Unix file path. Since 2048 was too long for a VARCHAR, I made it
TEXT. I since populated the table. Now I want to make the path
column a primary key, and I can't figure out how. (I googled the
web and groups without luck, looked over the reference manual also,
especially reading the entry on BLOBs.)
I was able to make a fulltext index with:
create fulltext index...
|
by: Neil |
last post by:
I've been discussing here a SQL 7 view which scrolls slowly when linked to
an Access 2000 MDB. After trying various things, I've distilled it down to
the following: when the linked view has a virtual primary key, it is slow;
when there is no virtual primary key, it scrolls quickly.
Looking at Profiler, I see that when there is no virtual primary key, Access
sends a simple select command to SQL Server. However, when there is a
virtual...
|
by: Abhi |
last post by:
FYI:
This message is for the benefit of MS Access Community. I found that
this prblem has been encounterd by many but there is hardly any place
where a complete solution is posted. So I thought I should give back
to the community by posting our findings.
Thanks you all for all your help till now by posting problems and
their solutions.
~Abhijit
|
by: sea |
last post by:
Is it a good idea to programatically create a primary key? For example
in a table called names, I have the following fields, (1) firstname
(2)lastname (3) ID
- will it be ok to create a primary key using for example the first 2
letters of the first name and the last 2 letters of the last name
AFTER the user enters the first and last names into a form? Maybe have
an invisible field on the form called ID that is linked to the id
field in...
| |
by: Michael Hannon |
last post by:
Greetings. We're running Postgres 7.3 on an Intel linux box (Redhat
Enterprise server, version 3.0). We find ourselves in an awkward
position: we have a database of attributes relating to students that
uses as its primary key the ID number of the student. This is awkward
for the following reasons.
Our university used to use social-security numbers for student ID's.
They stopped doing that a few years ago, but didn't force the change...
|
by: GGerard |
last post by:
Hello
I'm trying to find the best way to set indexes and primary keys on MSAccess
tables
What are the advantages and disadvantages of indexes and primary keys?
What fields should be indexed?
Should I index more than one field per table?
What fields should have the primary key?
|
by: Paul Hunter |
last post by:
I am new to databases and thus to Access. I have a situation where I am
trying to figure out how to key some tables I am working with. Consider that
I have a database of my own records which are invoices I work on. These
invoices are from four companies with their own invoice numbers. So, I
cannot key by invoice number because there is a likelihood of invoice
numbers duplicated by different companies. The records in this table of
joined...
|
by: newbtemple |
last post by:
New to programming and got a question. I'm trying to add a primary key in vb.net to a table I made in SQL. The table in SQL does not have a primary key. I pull that table into my program and concatenate two columns and assign a series of numbers from a for loop to rows with nulls, to make a third column that is unique enough to be a primary key.
This is where i'm getting stuck. I'm trying to figure out how to assign a primary key in VB...
|
by: marktang |
last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look !
Part I. Meaning of...
|
by: Hystou |
last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it.
First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
| |
by: tracyyun |
last post by:
Dear forum friends,
With the development of smart home technology, a variety of wireless communication protocols have appeared on the market, such as Zigbee, Z-Wave, Wi-Fi, Bluetooth, etc. Each protocol has its own unique characteristics and advantages, but as a user who is planning to build a smart home system, I am a bit confused by the choice of these technologies. I'm particularly interested in Zigbee because I've heard it does some...
|
by: agi2029 |
last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own....
Now, this would greatly impact the work of software developers. The idea...
|
by: isladogs |
last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM).
In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules.
He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms.
Adolph will...
|
by: conductexam |
last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one.
At the time of converting from word file to html my equations which are in the word document file was convert into image.
Globals.ThisAddIn.Application.ActiveDocument.Select();...
|
by: TSSRALBI |
last post by:
Hello
I'm a network technician in training and I need your help.
I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs.
The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols.
I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
|
by: adsilva |
last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
| |
by: bsmnconsultancy |
last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...
| |