[rambo123]

hi,
What is the difference between primary,secondary and composite key in sql.
what is the difference between varchar and varchar2.





technical support

[sk_kireeti]

Primary Key - Unique and not null
Secondary Key - Technically there is no such key. But if a table already has a primary key and if we need another key, make is a Unique key and we call it as Secondary key.
Composite Key - If more than 1 columns are participating together as primary key, then it is composite key.

Varchar Vs Varchar2 - No difference.

Thanks,
Krishna

[hightech]

Hi,

thanks I was actually searching for the difference between primary,secondary and composite key in sql.

[djbabu]

Originally Posted by sk_kireeti

Primary Key - Unique and not null
Secondary Key - Technically there is no such key. But if a table already has a primary key and if we need another key, make is a Unique key and we call it as Secondary key.
Composite Key - If more than 1 columns are participating together as primary key, then it is composite key.

Varchar Vs Varchar2 - No difference.

Thanks,
Krishna

Great and one little note on Varchar vs Varchar2

I n oracle 'Varchar' is going to be depricated or used for some other purpose and its a good practice to use varchar2 according to oracle Corp.

hope it helps