Answer / sathish

Assume a table contains columns
book name
author name
price

>>composite key

Having multi column primary key for a single table is known as composite key.

ex: primary composite key is book name and author name

>>primary Key

Primary key is the unique key, do not accept null value and used as a id to fetch the record from the table.

>> Foreign Key

A primary key of a table which is used as a reference key of another table..

Answer / saraswathi muthuraman

Compost key :

More than one column will be used to create compst key

SQL> create table ts_250 (a number,b number,c number,
primary key(a,c));

Table created.

here column A and column C is used to create compst key.
U can't insert null value in both columns.
Only unique combination of column A and column B value can
be inserted.

Primary key :

Key will be created on a single column in table.

SQL> create table ts_251 (a number,b number,c number,
primary key(a));

Table created.


null value cann't be inserted into column a.
oracle will create a index
only unique value can be inserted into column a.
only one primary key can be created on a table

Answer / saraswathi muthuraman

Compost key :

More than one column will be used to create compst key

SQL> create table ts_250 (a number,b number,c number,
primary key(a,c));

Table created.

here column A and column C is used to create compst key.
U can't insert null value in both columns.
Only unique combination of column A and column B value can
be inserted.

Primary key :

Key will be created on a single column in table.

SQL> create table ts_251 (a number,b number,c number,
primary key(a));

Table created.


null value cann't be inserted into column a.
oracle will create a index
only unique value can be inserted into column a.
only one primary key can be created on a table

Answer / reem

A primary key is a column which uniquely identifies the
records in a table.

A foreign key is a column (the child collumn) in a table
which has a corresponding relationship and a dependency on
another collumn (the parent collumn) that is usually in a
different table.

comosit key is more than one attribute can used as aprimary
key

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