what is the use of composite key?

Question

0.00/5 (No votes)

See more:

SQL-Server-2008

hi all, i have three tables,

1. master table

2. transaction table

3. master_transaction_link table

here my question is, in link table, which has id,mstrid,transid - mstrid is id of mster table and transid is id of transction table

why should i set the mstrid and transid as composite key in link table.?

what is the use of composite key in link table?

Posted 5-Dec-13 20:18pm

sangeetha m

Add a Solution

5 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Thomas ktg · Accepted Answer · 2013-12-05T20:34:00

Solution 1

This reference would probably give you the answer for your question.
Please refer here,
http://www.techopedia.com/definition/6572/composite-key[^]

Posted 5-Dec-13 20:34pm

Thomas ktg

Comments

[no name] 6-Dec-13 4:02am

thanks

Thanks7872 · Accepted Answer · 2013-12-05T20:36:00

See this : http://www.techopedia.com/definition/6572/composite-key[^]. It states that :

Quote:
A composite key, in the context of relational databases, is a combination of two or more columns in a table that can be used to uniquely identify each row in the table. Uniqueness is only guaranteed when the columns are combined, when taken individually the columns do not guarantee uniqueness.

TrushnaK · Accepted Answer · 2013-12-05T20:38:00

use of composite key is that:-
If you define primary key on two columns then columns can not take duplicate records.
composite key treat both of those columns as primary key.

eg. you have link table and that table has mstrid and transid columns. you have assign
primary key(mstrid ,transid) then they both columns can accept unique values.

mstrid transid
1 1001
2 1002
it allowed but you going to insert same record again in link table with same mstrid and transid then it is not allowed.

mstrid transid
1 1001

For more details read below links:-
http://weblogs.sqlteam.com/jeffs/archive/2007/08/23/composite_primary_keys.aspx[^]
http://www.techopedia.com/definition/6572/composite-key[^]

Peter Leow · Accepted Answer · 2013-12-05T21:43:00

Solution 4

Composite key is a primary key that makes up of 2 or more fields such as mstrid and transid in link table. It will ensure that every value pair of mstrid and transid in the link table is unique. Composite key is typically used as an intermediate table to link 2 tables that have many-to-many relationship.

Posted 5-Dec-13 21:43pm

Peter Leow

Comments

[no name] 6-Dec-13 4:02am

thanks for your answer.

Peter Leow 6-Dec-13 4:08am

You are welcome.

sangeetha m · Accepted Answer · 2013-12-05T23:12:00

Hi all , thanks for your valuable answers.,which help me to get clear in my concept. once again thanks for that.

Let i wanna be share my answer about composite key what i handled in my project.

in my project , there is neighborhood group and training program provided by government.

so, each group should attend one training program(lot of program) provided by government. here we must represent 1 to n relationship. and have an unique id for an each combination.

eg:

training program - master table
neighborhood group - transaction table

Master_Transanction_link

id traingId nhgoupId
1 1 1
2 1 2
3 1 3
4 2 1
5 2 2

so , each group can attend a single program provided by government.

what is the use of composite key?

5 solutions

Solution 1

Solution 2

Solution 3

Solution 4

Solution 5

Add your solution here

Preview 0