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GeekInterview.com > Interview Questions > Oracle > SQL
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| Question: What is difference between UNIQUE and PRIMARY KEY constraints?
Answer:
A table can have only one PRIMARY KEY whereas there can be any number of UNIQUE keys. The columns that compose PK are automatically define NOT NULL, whereas a column that compose a UNIQUE is not automatically defined to be mandatory must also specify the column is NOT NULL. |
| August 08, 2007 04:50:14 |
#7 |
| velsowmya |
Member Since: August 2007 Total Comments: 7 |
RE: What is difference between UNIQUE and PRIMARY KEY ...
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Primary key wont accept null values and a table can have only one primary key for a column.
Unique key accepts null values.A table can have any number of unique keys. |
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