Interested to Buy Any Domain ? << Click Here >> for more details...
what is primary key,unique key, foreign key? can u teach me
in simple language?
- 44 Answers
- 187545 Views
- Banking, CMC, CTS, HCL, Infosys, Keggfarms, SkyEss, Sunrise, TCS, Web Synergies, Wipro, I also Faced
- E-Mail Answers
Answer Posted / firoz basha
Primary key - Primary key means main key
def:- 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. for ex,
empno empname salary
1 firoz 35000
2 basha 34000
3 chintoo 40000
it will not the values as follows:
1 firoz 35000
1 basha 34000
chintoo 35000
Unique key - single and main key
A unique is one which uniquely identifies a row
of a table, but there is a difference like it will not
allow duplicate values and it will any number of allow
null values(In oracle).
it allows only a single null value(In sql server 2000)
Both will function in a similar way but a slight difference
will be there. So, decalaring it as a primary key is the
best one.
foreign key - a foreign key is one which will refer to a
primary key of another table
for ex,
emp_table dept_table
empno empname salary deptno deptno deptname
In the above relation, deptno is there in emp_table which
is a primary key of dept_table. that means, deptno is
refering the dept_table.
| Is This Answer Correct ? | 1165 Yes | 93 No |
Post New Answer View All Answers
how can we view column head in first page but not in remaining pages?
When should you not use firebase?
What is ole db provider for sql server?
What are database connection details?
Does facebook use graph database?
What is database schema name?
How does non-cluster index functions?
Differentiate between unique key and foreign key?
Write a query to retrieve for many to many relationships?
What do you mean by foreign key and primary key?
During insert operation in Netezza Connector, if we give direct option as Yes , is there any issue?
WHAT IS NEED BY METION DATFMT AND TIMFMT IN H-SEPICITION IN RPGLE?
What is the Difference Primary key and Unique Key
What is the relationship that exists inside in E-R diagram?
can any one tell me how i can start database testing mean what should be initial point and how i can write a query for listing page of any item thanks in advance
