What is an Index, Primary Key and Foreign Key? When do one use index?

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Guest

  • Jan 6th, 2007
 

primary key is a candidate key (out of many candidate keys)that is chosen by DB designer to identify entities in an entity set.

simply v can say that it is used to identify a row uniquely.( eg ur roll number is a primary key)

Foreign key- is a column or columns whose values are the same as the primary key of another table.

                 - help in joining two tables

                  -  v can think  it as a copy of primary key from another relational table.

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Guest

  • Jan 6th, 2007
 

Index key

An index key orders one or more table columns (keys). It has attributes such as being unique or primary, a comparison specification for text columns, and a list of columns which make up the key

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vmshenoy

  • Jan 6th, 2007
 

Primary key is a candidate key (out of many candidate keys),that is chosen by DB designer to identify entities in entity set.
 Thatis it is used to identify rows uniquely.

Foreign Key is a -column or columns whose values are the same as primary key of aother table.
                          -helps in joining tables
                           - is a copy of primary key from another relational table.

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vmshenoy

  • Jan 6th, 2007
 

An index key orders one or more table columns (keys). It hasattributes such as being unique or primary, a comparison specification for textcolumns, and a list of columns which make up the key.

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