Creating Database Index

Indexes are used to arrange records in a proper manner in database using references to the data. This helps in the searching of records whenever a complex Select query is fired which involves searching multiple table. In case no index is created a full table scan is performed, which increases the response time, hence reduces performance.

Note: Indexes are created on columns which are meant for searching the data.

Index can be of two types:

  • Unique Index: These are automatically created by the database whenever any primary key or unique constraint is imposed on a column. It is also called as Implicit Index.
  • Non-Unique Index: These indexes are explicitly created by the users.

Creating an Index

Sytax to Create Index:

Note: An index created on a single column is called as simple index, and an index created on multiple columns is called as complex index.



The 1st example above is an example of simple index and the 2nd one is of complex index.

Dropping an Index


Note: An index also gets deleted when a table or a column having the index is dropped.

Disadvantages of Index

A Database index does have some disadvantages:

  • They decrease performance on inserts, updates, and deletes.
  • Being objects they take up space.

Thus an index should only be created when they are actually needed.


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