Index in sql is created on existing tables to retrieve the rows quickly.
----> When there are thousands of records in a table, retrieving information will take a long time. Therefore indexes are created on columns which are accessed frequently, so that the information can be retrieved quickly.
---->Indexes can be created on a single column or a group of columns.
---->When a index is created, it first sorts the data and then it assigns a ROWID for each row.Example:
CREATE INDEX index_name
ON table_name (column_name1,column_name2...);