Can we use more than one null value for unique key?
- 31 Answers
- 56820 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
How is a PL/SQL code compiled?
What do you mean by stored procedures? How do we use it?
what is a cursor? : Sql dba
What is audit logout in sql profiler?
What is a call statement? Explain with an example.
What does count (*) mean in sql?
What is sqlservr exe?
what is not null constraint? : Sql dba
What does partition by mean in sql?
what is transaction? : Sql dba
Can we create foreign key without primary key?
What is normalization in sql?
What do you understand by pl/sql packages?
What are sql data types?
What is pl sql quora?
