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Can we use more than one null value for unique key?
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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 |
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