Create index syntax on MongoDB

Create index on employees table with column employee_id in ascending order.

--Create index on employees table with column employee_id in ascending order
db.employees.ensureIndex( { emp_id: 1 } )


Create index on employees table with column emp_id and age(desc order)

db.employees.ensureIndex( { emp_id: 1, age: -1 } )


Example of SQL query for RDBMS database e.g Oracle, SQL Server

-- Create index in SQL query with one column ascending order.
create index on idx_emp on employees (emp_id);

--Create index in SQL query with ascending or descending order.
create index on idx_emp1 on employees(emp_id,age desc);


Drop index in MongoDB

db.collection.dropIndex(index)

-- Example drop index employee_id_idx on employees table.
db.employees.dropIndex("emp_id_idx")

-- Drop index with column name specification as created first index in this blog.
db.pets.dropIndex( { "emp_id" :1 } )


Get the list of index present on collection/table

db.collection.getIndexes()

Example:
-- Get list of indexes present on employees table
db.employees.getIndexes()