Creation of index on table depends on size of table, volume of data.
If table size is large and we need only few data while selecting data then create index. How frequently column is used in where condition, its also important.
if table has already a primary key, then create a unique key for the required column. Creating a primary key or unique key automatically create unique index on the column.
It is also not advised to create so many indexes as it impacts on query performance of DML statments as every DML statment need to go through with various index and table segments simultaneously.
We can create index or rebulid online also. It enables us to update base tables on the sametime.
creating any index parallelly is not supported while creating and rebuilding index online.
If table size is large and we need only few data while selecting data then create index. How frequently column is used in where condition, its also important.
if table has already a primary key, then create a unique key for the required column. Creating a primary key or unique key automatically create unique index on the column.
It is also not advised to create so many indexes as it impacts on query performance of DML statments as every DML statment need to go through with various index and table segments simultaneously.
We can create index or rebulid online also. It enables us to update base tables on the sametime.
creating any index parallelly is not supported while creating and rebuilding index online.
CREATE INDEX idx_emp_mgr ON employee (empid,mgrid) ONLINE;
