Category Archives: MongoDB

Manage index syntax on MongoDB

Leave a reply

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()

Create/alter/drop table(collection) in MongoDB

Leave a reply

Syntax for managing the table collection in MongoDB 

Create table(collection) in MongoDB

-- For Create table in MongoDB:

db.employees.insert( {
emp_id: “RAM”,
age: 50,
status: “A”
} )

Or

db.createCollection(“employees”);

Example of Create Table in SQL in RDBMS databases:

CREATE TABLE employees( id MEDIUMINT NOT NULL  AUTO_INCREMENT,
emp_id Varchar(30),
age Number,
status char(1),
PRIMARY KEY (id) )

Add column in collection of MongoDB

-- Add the join_date column in employees collection.

db.employees.update(
{ },
{ $set: { join_date: "" } },
{ multi: true }
)

Example show add column in SQL RDBMS database:

ALTER TABLE employees ADD join_date DATETIME

Remove column in MongoDB:

-- Remove the join_date column from employees table

db.employees.update(
{ },
{ $unset: { join_date: "" } },
{ multi: true }
)

Example Remove column in SQL RDBMS:

alter table employees drop column join_date;

Drop collection in Mongdb:

-- Drop table employees.

db.employees.drop();

Example for RDBMS database:

drop table users:

Use of Delete query in MongoDB

Leave a reply

Example of Delete query in MongoDB

Delete specific rows from the MongoDB
Delete specific data from tables(collection)

--In SQL query
DELETE FROM employees WHERE status = "D"

–In MongDB Query:
db.employees.remove( { status: “D” } )

Example:
Delete records from employees table which having status column value equal to N

-- Remove from employee collection
db.employees.remove( { status: "N" } )
Output:
WriteResult({ "nRemoved" : 1 })

Delete all data from table(collection)
Remove all data from MongoDB

-- In SQL Query in RDBMS
DELETE FROM employees;

— In MongoDB query:
db.employees.remove({})