| Primary key Vs Unique+Not null [message #370418] |
Wed, 22 September 1999 15:14  |
atul
Messages: 17
Registered: September 1999
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Junior Member |
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Pls let me know the difference :
if two tables having same 2 fields
suppose emp_no number(3)
emp_name varchar2(30)
in one table I take emp_no as a primary key
and in other table I take emp_no as a Unique+not null
Thanks.
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| Re: Primary key Vs Unique+Not null [message #370423 is a reply to message #370418] |
Wed, 22 September 1999 17:24  |
m a sivan
Messages: 34
Registered: July 1999
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Member |
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well its same if u do exactly how u are explaining
as far as data etc is concerned but sometimes people use a composite primary key and some field as unique.
Also if u declare something as a primary key an automatic index is created which is not true when u declare it as unique and not NULL.
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| Re: Primary key Vs Unique+Not null [message #370453 is a reply to message #370418] |
Sun, 26 September 1999 13:05 |
sonik chopra
Messages: 4
Registered: September 1999
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Junior Member |
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hi atul,
if you do so in case of single field it will not affect.but it will drastically change the constraint in case of combined primary key.try to make a primary key(composite) on one table,do the same thing on another table by giving more than two collumns unique & not null & see the result by yourself.
keep in touch,
sonik
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