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what are the advantages of primary key over unique+notnull
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Answer / tulsi
Primary key will avoid duplicate and null values in a table
which the combination of unique+not null will do.But the
advantage is,if a table has primary key we can create
relation to child tables.
| Is This Answer Correct ? | 28 Yes | 13 No |
Answer / shilpa.oracle
Primary key accepts only unique values and does not allow
null values.
Unique key accepts unique values and allows null values.
not null constraint allows duplicate values and doesnt allow
null values.
When a primary key constraint or unique key constraint is
created by default index is created on the columns with
these constraints.
| Is This Answer Correct ? | 16 Yes | 4 No |
Answer / smita
A Foriegn key can refer to the primary key.
A Foriegn key can refer to the unique key also .
| Is This Answer Correct ? | 14 Yes | 6 No |
Answer / soubhagya
When we create a primary key automatically a cluster index
is created on those columns involved in primary key.But
this index not created in unique+not null key, it only
restrict the duplicate values.
| Is This Answer Correct ? | 4 Yes | 3 No |
Answer / kamal
we are able to create a primary key for combination of more
than 1 column. which is not possible in Unique,we should
create unique key for each and every column in the table
individually.
ex . we can create a primary key for (Name,DOB,address)- ie
combination of these three columns be unique.
| Is This Answer Correct ? | 3 Yes | 5 No |
Answer / charumathi
Unique-Duplicates not allowed
Nulls allowed
Not null-NUlls not allowed
Primary key-No Duplicates
No Nulls
A Foriegn key can refer to the primary key.
| Is This Answer Correct ? | 4 Yes | 7 No |
Answer / nitesh
PRIMARY KEY CREATED WITH INDEXES WHICH IS NOT HAPPEN WITH
UNIQUE AND NOT NULL
| Is This Answer Correct ? | 8 Yes | 21 No |
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