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What is the difference between primary key & unique index ?
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Answer / shankar
Primary Key cannot have NULL values in it wherein an
UNIQUE index can have one NULL value in it.
| Is This Answer Correct ? | 37 Yes | 3 No |
Answer / mani
Primary key can be defined only one for a table whereas
number of unique indexes can be defined for a table.
primary key can not have null values but unique can have
null values and to remind one null value can never be equal
to another null value.
| Is This Answer Correct ? | 23 Yes | 4 No |
Answer / uddipto banerji
1. Primary Key is a column or a set of columns that uniquely identifies a row.Its purpose RECORD UNIQUENESS
2. Primary Key will not allow duplicate values.
3. Primary Key will not allow null.
4. Primary Key is not compulsory but recommended.
5. Primary Key helps to identify one record from another.
6. Only One Primary Key is allowed per table.
7. Unique Indexes is created automatically if there is Primary Key.
8. One table can combine upto 16 columns in a Composite Primary Key.
9. A table can have more than one Unique Key which is not possible in a Primary Key.
| Is This Answer Correct ? | 10 Yes | 2 No |
Answer / palash ghosh
1)Primary key creates an implicit culstered index on a
table, unique key does not create any implicit index.
2)Columns defined as primary key does not allow null values,
where as columns defined as unique can allow null values.
3)A table can have just one primary key (can be a composite
key) where as there can be multiple unique columns (keys).
4)Primary key is a unique key with the above mentioned
features.
| Is This Answer Correct ? | 9 Yes | 1 No |
Answer / mehdee
- Each primary key must associate with a unique index, but
unique index dose not have to associate to the primary key.
| Is This Answer Correct ? | 6 Yes | 3 No |
Answer / s
Primary Key uniquely identifies the record and the UNIQUE
index on the primary key ensures that no duplicates values
will be stored in the table.
| Is This Answer Correct ? | 16 Yes | 14 No |
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