An index is a object which is used to improve performance during retrieval of records.
It helps to retrieve the data quickly from the tables.
When column contains a large number of NULL values, then we can create Index.
It a structure that provides faster access to the rows of a table based on the values of one or more columns.
It stores data values and pointers to the rows where those data values occur.
If a table is very small, then we cannot create Index.
Indexes are very useful and make the data access very fast.
Syntax: CREATE INDEX index_name ON table_name;
Example
CREATE UNIQUE INDEX emp_ename_index
ON Employee(Ename);
In the above example, the UNIQUE keyword is used when combined values of index should be unique. It does not allowed duplicate values to be inserted into the table.
We created an Index on Employee name (Ename) column in the Employee table.
Indexes can be dropped explicitly using the DROP INDEX command.
