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GeekInterview.com > Interview Questions > Oracle > SQL Plus
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Question: What is the basic difference between primary key and (unique key along with Not NULL).
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| May 05, 2008 11:13:38 |
#9 |
| ramesh_bollapragada |
Member Since: May 2008 Total Comments: 1 |
RE: What is the basic difference between primary key and (unique key along with Not NULL).
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hi every one
differences
1) primary key is defined only on one column where as unique + not null can be defined on many columns
2) we can define the relationship ( master detail relationship) with references to unique+not null column but it is not possible to remove the relationship with
alter table <tablename> primary key cascade. Because Unique + Not null is not exactly primary key
3) When you refer the data dictionery , with unique and not null it is going to create to different constraints where as with primary key it is going to create one constraint.
Regards
Ramesh B |
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