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what is primary key?

Answers were Sorted based on User's Feedback



what is primary key?..

Answer / ramprakash

A primary key is used to uniquely identify each row in a
table

Is This Answer Correct ?    23 Yes 4 No

what is primary key?..

Answer / guest

a key is defined unique and not null in a column is called
primary key

Is This Answer Correct ?    17 Yes 1 No

what is primary key?..

Answer / guest

It is a combination of unique and notnull

Is This Answer Correct ?    10 Yes 0 No

what is primary key?..

Answer / vinod singh kushwah

A primary key is used to uniquely identify each row in a
table. It can either be part of the actual record itself ,
or it can be an artificial field (one that has nothing to
do with the actual record). A primary key can consist of
one or more fields on a table. When multiple fields are
used as a primary key, they are called a composite key.
Primary keys can be specified either when the table is
created (using CREATE TABLE) or by changing the existing
table structure (using ALTER TABLE).
Below are examples for specifying a primary key when
creating a table:

MySQL:

CREATE TABLE Customer
(SID integer,
Last_Name varchar(30),
First_Name varchar(30),
PRIMARY KEY (SID));

Oracle:

CREATE TABLE Customer
(SID integer PRIMARY KEY,
Last_Name varchar(30),
First_Name varchar(30));

SQL Server:

CREATE TABLE Customer
(SID integer PRIMARY KEY,
Last_Name varchar(30),
First_Name varchar(30));
Below are examples for specifying a primary key by altering
a table:

MySQL:

ALTER TABLE Customer ADD PRIMARY KEY (SID);

Oracle:

ALTER TABLE Customer ADD PRIMARY KEY (SID);

SQL Server:

ALTER TABLE Customer ADD PRIMARY KEY (SID);

Is This Answer Correct ?    6 Yes 1 No

what is primary key?..

Answer / arkchowdary

primary Key ----------- It is used to uniqely identify
each row in a table.

It is a combination of unique and Notnull.

A primary key can consist of one or more fields on a table.
When multiple fields are
used as a primary key, they are called a composite key.

Is This Answer Correct ?    4 Yes 0 No

what is primary key?..

Answer / sajeda

it is defined as the candidate key that is selected to
identyfi tuple uniqly within a relation.
* it is not contain null value.

Is This Answer Correct ?    4 Yes 0 No

what is primary key?..

Answer / kiran

to simply answer this question - a primary key is something
which has both unique and not null constraints on the
colums-table

Is This Answer Correct ?    2 Yes 0 No

what is primary key?..

Answer / dhanu

A column that has completely unique data throughout the
table is known as Primary Key.

Is This Answer Correct ?    3 Yes 2 No

what is primary key?..

Answer / parthiban.s

primary Key is a unique one.in a table only one primary
key is available. it;s not accepted null values

Is This Answer Correct ?    1 Yes 2 No

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