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what is the difference between primary key & foreign key?
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Answer Posted / raffi.shaik
Primary key is unique
primary key is not NULL and
foreign key is NULL
foreign key reference as Primary key in another table
Primary key is unique key but foreign key always refers to
primary key
primary key is used to identify a row and it does not allow
null values. It avoids duplication of rows.
whereas foreign key refers to a column or combination of
columns included in the definition of referential integrity.
In the context of relational databases, a foreign key is a
referential constraint between two tables.[1] The foreign
key identifies a column or a set of columns in one
(referencing) table that refers to a column or set of
columns in another (referenced) table. The columns in the
referencing table must form a primary key or unique key.
| Is This Answer Correct ? | 1 Yes | 0 No |
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i have a question here... As of my knowledge, when we apply an index (b-tree)on a column, internally it arranges the data in b-tree format and do the fetching process correspondingly... and my quetion is... How a bit-map index arranges the data internally when applied on a column?IS it in b-tree format or whatelse?
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