Interested to Buy Any Domain ? << Click Here >> for more details...
Can we use more than one null value for unique key?
- 31 Answers
- 65453 Views
- A1 Technology, Wipro, I also Faced
- E-Mail Answers
Answer Posted / praveen hr
UNIQUE Constraints
You can use UNIQUE constraints to make sure that no
duplicate values are entered in specific columns that do
not participate in a primary key. Although both a UNIQUE
constraint and a PRIMARY KEY constraint enforce uniqueness,
use a UNIQUE constraint instead of a PRIMARY KEY constraint
when you want to enforce the uniqueness of a column, or
combination of columns, that is not the primary key.
Multiple UNIQUE constraints can be defined on a table,
whereas only one PRIMARY KEY constraint can be defined on a
table.
Also, unlike PRIMARY KEY constraints, UNIQUE constraints
allow for the value NULL. However, as with any value
participating in a UNIQUE constraint, only one null value
is allowed per column.
A UNIQUE constraint can be referenced by a FOREIGN KEY
constraint.
Link from MSDN http://msdn.microsoft.com/en-
us/library/ms191166.aspx
| Is This Answer Correct ? | 2 Yes | 1 No |
Post New Answer View All Answers
What is sql and how does it work?
What is localdb mssqllocaldb?
How to place comments in pl/sql?
what is oltp (online transaction processing)? : Sql dba
What does := mean in pl sql?
what is acid property in database? : Sql dba
Is sql free?
Name three sql operations that perform a sort.
What is a sql driver?
What is sqlite format?
what is meant by nl2br()? : Sql dba
What is the difference between jpql and sql?
What is numeric function sql?
What is oracle pl sql developer?
What is sql dialect?
