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What is the main different between Null and NOT Null.
Difference between Primary and Unique Key.
How to Check the database from which application is it
possibe.
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Answer / kalpana
Primary key can never be NULL.it is used to uniquely
identify the row in a table.The database engine requeir a
value to relocate the record.so Primary key can never be
NUL.unique key may be NULL.
| Is This Answer Correct ? | 21 Yes | 0 No |
Answer / sunil kumar
Hello Nivedita,
I am not satisfied with ur answer the difference between
primary key and foreign key.I think the answer is reverse.
| Is This Answer Correct ? | 15 Yes | 1 No |
Answer / bharanikumar
primary key does not allow null value,
but unique allow only one null value...
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| Is This Answer Correct ? | 6 Yes | 0 No |
Answer / amit kumar tiwari
primary key uniquely define each table and never allow NULL
value. But unique key may be NULL value.
| Is This Answer Correct ? | 2 Yes | 1 No |
Answer / g priya
If a field is null the database engine makes the field to be 0
if not null is specified ,field must be given a value
Primary key is unique,not null,index where as Unique key has
1 null value
| Is This Answer Correct ? | 2 Yes | 5 No |
Answer / nivedita
IF NULL is specified,the feild is allow to be left empty
without any value.
IF NOT NULL is specified,the field must be given a value. In
the absence of either a NULL or NOT NULL, NULL is assumed.
-------
Unique key can't be NULL.Primary key can be NULL.
Unique key always contain unique value,duplicate are not
allowed(genrally the system genrated key).Primary key maybe
repeated.
| Is This Answer Correct ? | 6 Yes | 35 No |
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