Answer / ashis kumar jena

A primary key is one which uniquely identifies a row
of a table.
This key does not allow null values and also
does not allow duplicate values.
Each table should have a primary key, and each table can
have only one primary key.

Answer / perumal

1. Primary Key Doesn't allow the NULL values and also
does not allow duplicate values.

2. Primary Key has the Unique Columns.

3. Primary Key Uniquely Identify the each row of the tables.

Answer / hannan oca

primary key =notnull+unique value in column

a table consist of only one primary key.

Example

a primary key is like a father in house, like only one but
there may be a lot of childs just like columns.

Answer / satheeh

Primary key is nothing but restriction or condition or constraint given to a specific column to avoid the null and duplicate values.
primary key=not null+unique
that means primary key performs both operations at a time.
primary key plays vital role when relationship between two or more tables

i have xml source. xml source having lacks of records. i want extract/retrive xml source data using sql query. please tell me how to write query.

4 Answers   TCS,

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