Primary keu & UNique Key

[Former Member]

Hi all,

Is there any difference between primary key and unique key.

thanks

Aashish

[Former Member]

The Main difference is that Unique Key allows null value but Primary Key doesn't allow null values.

thats it.

[former_member188685]

Primary key and Unique Key Both are same

regards

vijay

[Former Member]

aashish,

As you can see, all of the developers on this thread have DB installations that do not permit non-unique primary keys.

Please check with your DBAs to see if yours does... as unique and primary keys are NOT truly the same. Oracle, for example, will permit non-unique primary keys. It is NOT the "suggested" model... but it is possible.

Please reward points accordingly and close the thread.

[Former Member]

Hi,

Pls award points to useful answers.

Regards,

Amit M.

[abdul_hakim]

Hi,

Primary is used to uniquely identify the records in the table.Primary key is a Unique key by default.

<b>If there is a primary key then there is a unique key.

If there is a unique key then there is a primary key.</b>

Thanks,

Abdul

[Former Member]

Hi aaahish,

1. This concept of primary key and unique key

comes into picture at the database level

(especially oracle)

2. The only difference is that

unique key allows

insertion of a NULL value

into the key field(s)

Where as primary key does not allow.

3. Similary is ;

Both maintain unique/distinct values

in the table.

I hope it helps.

regards,

amit m.

[Former Member]

Hi aashish,

<b>Primary key</b>

Both are same.<b>A primary key is usually called as an unique key</b>.A primary key is defined for each database table. A user-defined primary key can consist of one or more columns.<i>The primary key must have a unique value for each table row.</i> The primary key is either defined by the database user, or generated internally.

<b>

Foreign key</b>

If the values in a column (or a combination of columns) of a table always match the values of the primary key column of another table, then this column (or combination of columns) is called a foreign key.

Hope this helps u,

Regards,

Nagarajan.

[Former Member]

A primary key is the "key" used to store a record in a database. Depending on how your DB is set-up, it can or can not be unique. It SHOULD BE, but it is not a requirement in all DBs.

A unique key is TRULY a unique (meaning no other records in the table will have the same key field values).

Reward points accordingly.

[Former Member]

Bear in mind that this statement is not true on all DB installations - "The primary key must have a unique value for each table row."

Check with your DBAs to verify of your DB installation permits non-uniue primary keys. Again, it is NOT a good practice to do this... but some DB systems will permit it and some customers ACTUALLY use that functionality. I would NOT... but some do.