SQL for MongoDB

Introduction to SQL for MongoDB

SQL, or Structured Query Language, is utilized to manage and manipulate data in relational databases. In contrast, MongoDB is a document-oriented NoSQL database that stores data in JSON-like documents instead of tables with predetermined rows and columns.

Although MongoDB doesn't use SQL, it has its query language, MongoDB Query Language (MQL), which has some similarities to SQL but also some significant differences. Despite the difference in their underlying data models, SQL and MQL share many common concepts and commands. To facilitate the translation of SQL queries into equivalent MQL queries, MongoDB provides a SQL to MongoDB Query Translator. This tool allows developers to use SQL commands like SELECT, WHERE, ORDER BY, LIMIT, and JOIN to query MongoDB databases. However, due to the different underlying data models, not all SQL commands will be translatable, and there will be limitations to the translation.

Now let us look at an example of how with the help of the translator we can use SQL to query Mongthe oDB database:

Example:

**Explanation **

This SQL query selects the name and email columns from the users collection where the age is greater than 40, orders the results by name in ascending order, and returns only the first 20 results.

The corresponding MQL query generated by the translator would look like this:

Explanation :

As you can see, the MQL query is quite different from the original SQL query, but it accomplishes the same task. With a little bit of practice and familiarity with MQL syntax, you can easily translate your SQL knowledge to work with MongoDB.

SQL to MongoDB Mapping

One of the most important differences between SQL and MongoDB is the way they handle data. In SQL, data is organized into tables with predefined columns and rows, whereas in MongoDB, data is stored in flexible, hierarchical documents. This difference means that SQL and MongoDB have different syntaxes and functionality.

Despite these differences, there are some basic mappings between SQL and MongoDB that can help developers translate their SQL knowledge to work with MongoDB. For example, the SELECT statement in SQL can be translated to the find() method in MongoDB, and the WHERE clause in SQL can be translated to the query parameter in the find() method.

Here are some SQL terms and ideas, which are comparable to those used by MongoDB, which are shown in the table below.

Example Showing Similar Statements in SQL and MongoDB

Let us take an example of a table assuming the given conditions:

• In the example, the SQL table is termed as Students.
• In the example, the MongoDB collection is termed as Students, which contains documents of the following prototype.

Here are some common SQL statements and their MongoDB equivalents:

Create and Alter commands

MongoDB and SQL Insert Statement

SQL and Mongo DB Select Command

SQL and MongoDB Update Statements

SQL and MongoDB Delete Statements

Create and Alter commands

SQL CREATE Command: The CREATE command in SQL is used to create a new table, view, index, or database. The syntax for the CREATE command in SQL is as follows:

Syntax:

Example:

For example, to create a table named employees with columns id, name, age, and salary in SQL, the CREATE command would be:

SQL ALTER Command: The SQL ALTER command is utilized to make changes to the structure of a table that already exists. The ALTER command's syntax in SQL is given below:

Syntax:

Example:

For example, to add a new column gender to the employees table created above, the ALTER command would be:

MongoDB CREATE Command:

In MongoDB, the CREATE command is employed to establish a new database or collection.The CREATE command syntax in MongoDB is given below:

To create a new database in MongoDB, use the following command:

Syntax:

Example:

For example:

To create a new collection in MongoDB, use the following command:

Syntax:

Example:

For example, to create a collection named employees in MongoDB, the command would be:

MongoDB ALTER Command: In MongoDB, the ALTER command is not used to modify the structure of an existing collection. Instead, you can insert new documents into the collection or update existing documents with new fields or values. The syntax for inserting a new document into a collection in MongoDB is as follows:

Syntax:

Example:

For example, to insert a new document into the employees collection created above with fields name, age, and salary, the command would be:

To update an existing document in MongoDB, use the update() method with the $set operator to set new values for a field. For example, to update the salary of the employee with the name "John Doe" to 60000, the command would be:

Insert Commands in SQL and MongoDB

SQL Insert Command: The INSERT command in SQL is used to insert new records into an existing table. The syntax for the INSERT command in SQL is as follows:

Syntax:

sql

INSERT INTO [TABLE NAME] (col1, col2, col3,...) VALUES (val1, val2, val3,...);

Example:

For example, to insert a new record into the employees table created above with values for the columns id, name, age, and salary, the command would be:

Note that the values need to be in the same order as the columns specified in the INSERT command.

MongoDB Insert Command: In MongoDB, the INSERT command is used to insert new documents into a collection. The syntax for the INSERT command in MongoDB is as follows:

Syntax:

Example:

For example, to insert a new document into the employees collection created above with fields name, age, and salary, the command would be:

Note that the fields and values need to be specified as JSON objects. Also, if the collection does not exist, MongoDB will create it automatically when the first document is inserted.

SELECT Commands in MongoDB and SQL

The SELECT command retrieves data from a database table and enables users to specify the columns they want to retrieve, as well as apply filters and sorting to the data. This command is supported by numerous database management systems, including SQL and MongoDB.

SELECT Commands in SQL: The SELECT command in SQL is used to retrieve data from one or more tables in a database. The syntax for the SELECT command in SQL is as follows:

Syntax:

The column1, column2, ... parameters are used to specify which columns should be returned in the query results. If the * character is used instead of column names, all the columns in the table will be returned.

The table1 parameter is used to specify which table the data should be retrieved from.

The WHERE clause specifies the filter criteria for data retrieval and is an optional parameter. If it is not provided, all rows in the table will be returned.

Example:

For example, suppose we have a table named employees in SQL, and we want to retrieve all the employees that have a salary greater than 50000. We can use the following command:

The following command will retrieve all rows from the "employees" table where the salary is greater than 50000.

SELECT Commands in MongoDB: In MongoDB, the equivalent of the SQL SELECT command is the find() method, which is used to retrieve documents from a collection. The syntax for the find() method in MongoDB is as follows:

Syntax:

The query parameter is used to specify the filter criteria for the data retrieval. It is an optional parameter, and if it is not provided, all the documents in the collection will be returned.

The projection parameter is used to specify which fields should be returned in the query results. It is also an optional parameter, and if it is not provided, all the fields in the documents will be returned.

Example:

For example, suppose we have a collection named users in MongoDB, and we want to retrieve all the documents that have the age field greater than 30. We can use the following command:

This command will return all the documents in the users collection that have an age field greater than 30.

In summary, the SELECT command is used to retrieve data from a database table in both MongoDB and SQL. The syntax and usage of the command may vary slightly between these two database management systems, but the basic concepts and principles remain the same.

MongoDB and SQL Update Commands

Update commands are used to modify or update existing data in a database table or collection. Both MongoDB and SQL support update commands, although the syntax and usage of these commands may vary between the two database management systems.

UPDATE Commands in SQL: In SQL, the update command is implemented using the UPDATE statement. The syntax for the UPDATE statement is as follows:

Syntax:

The table_name parameter is used to specify the name of the table that should be updated.

The column1 = value1, column2 = value2, ... parameter is used to specify the modifications to be made to the rows that match the condition.

The WHERE clause is used to specify which rows should be updated. If the WHERE clause is not specified, all the rows in the table will be updated.

Example:

For example, suppose we have a table named employees in SQL, and we want to update the salary of all the employees who have the job title Manager. We can use the following command:

This command will update the salary of all the employees who have the job title "Manager" to 60000.

UPDATE Commands in MongoDB: In MongoDB, the update command is implemented using the update() or updateMany() method. The syntax for the update() method is as follows:

Syntax:

The query parameter is used to specify which documents should be updated. It can be any valid query expression.

The update parameter is used to specify the modifications to be made to the documents that match the query expression. It can be any valid update expression.

The upsert parameter is an optional parameter that specifies whether a new document should be inserted if the query expression does not match any existing documents.

The multi-parameter is an optional parameter that specifies whether multiple documents should be updated if the query expression matches more than one document. If the multi parameter is set to false or not specified, only the first document that matches the query expression will be updated.

Example:

For example, suppose we have a collection named "users" in MongoDB, and we want to update the age of all the users who have the last name "Smith". We can use the following command:

This command will update the age of all the users who have the last name "Roger" to 45.

In summary, both MongoDB and SQL support update commands that allow users to modify existing data in a database table or collection. The syntax and usage of these commands may vary between these two database management systems, but the basic concepts and principles remain the same.

SQL MongoDB Delete Commands

Delete commands are used to remove data from a database table or collection. Both MongoDB and SQL support delete commands, although the syntax and usage of these commands may vary between the two database management systems.

Delete commands in SQL: In SQL, the delete command is implemented using the DELETE statement. The syntax for the DELETE statement is as follows:

Syntax:

The table_name parameter is used to specify the name of the table from which data should be deleted.

Which rows should be deleted is specified by the WHERE clause. If the WHERE clause is not specified, all the rows in the table will be deleted.

Example:

For example, suppose we have a table named employees in SQL, and we want to delete all the employees who have the job title Intern. We can use the following command:

This command will delete all the rows in the employees table that have the job title Intern.

Delete commands in MongoDB: In MongoDB, the delete command is implemented using the deleteOne() or deleteMany() method. The syntax for the delete() method is as follows:

Syntax:

The filter parameter is used to specify which document should be deleted. It can be any valid query expression.

The writeConcern parameter is an optional parameter that specifies the level of acknowledgment requested from MongoDB for write operations.

The syntax for the deleteMany() method is similar to deleteOne(), but it deletes multiple documents that match the query expression.

Example:

For example, suppose we have a collection named "users" in MongoDB, and we want to delete all the users who have the last name "Roger". We can use the following command:

This command will delete all the documents in the users collection that have the last name Roger.

In summary, both MongoDB and SQL support delete commands that allow users to remove data from a database table or collection. The syntax and usage of these commands may vary between these two database management systems, but the basic concepts and principles remain the same.

SQL MongoDB Queries

While SQL is a language used for querying relational databases, MongoDB uses a different query language that is based on JSON-like documents. However, MongoDB does provide some support for SQL queries through the use of the MongoDB Connector for BI.

The MongoDB Connector for BI allows users to connect to MongoDB data using SQL-based tools and applications. This connector provides a SQL interface to query MongoDB data, allowing users to use SQL syntax to perform queries against a MongoDB database.

To use SQL with MongoDB, you must first install and configure the MongoDB Connector for BI. Once you have done that, you can use any SQL-based tool or application to connect to your MongoDB database and perform queries.

For example, suppose we have a collection named employees in MongoDB, and we want to retrieve the first name, last name, and salary of all the employees who have the job title Manager using SQL syntax. We can use the following SQL query:

This SQL query is similar to the MongoDB query we discussed earlier:

Note that while SQL can be used with MongoDB through the MongoDB Connector for BI, it is still recommended to use MongoDB's native query language for optimal performance and functionality. The use of SQL should be reserved for cases where it is necessary to integrate with existing SQL-based tools or applications.