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
- 186381 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
where can i free download sqlserver2008..i can install sqlserver2008 without visual studio 2008 and work on it
What is the Lock Based Protocol used for?
How is image stored in database?
What are database connection details?
How to do Data size testing? Who does this testing (Developer or tester)?
diff b/w inter process and in process
Can you create a database in word?
What does new grouping sets enables you to do?
i applied prompt on country when i run report it shows list of all countries but want it to show only four countries name
Explain phantom deadlock?
What is the difference between data source and database?
i have windows-xp processor with P4 system. whenever I tried to download foxpro for windows 2.6 on windows XP, my operating system failed to install foxpro for windows 2.6.please. how could i download , install & run foxpro for windows 2.6 easily on windows XP ?
how do you do sql tuning?
What are the various ways to execute a query in teradata?
1. How to test Database? Please, give me all details for "SQL,Msaccess, Mysql Database? 2.For which functionalities database used? 3.How to convert Guest to Admin by Mysql database?
