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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. |
| October 10, 2007 03:18:50 |
#8 |
| Rahul Kataria |
Member Since: Visitor Total Comments: N/A |
RE: What is difference between UNIQUE and PRIMARY KEY ...
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Primary key cannot take null values but Unique can take null values
simply we can say
primary key = unique + not null |
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