Everything Dev Needs to Know About SQL Server JSON Data Type

Hello Dev, welcome to this comprehensive guide about SQL Server JSON data type. JSON data type is one of the most convenient data types for storing and manipulating data in modern computer systems. In this guide, we will cover everything you need to know about SQL Server JSON data type from basics to advance topics. So, sit back, relax, and let’s dive in.

Introduction to JSON Data Type

JSON (JavaScript Object Notation) is a lightweight, text-based, and language-independent data interchange format that is easy for humans to read and write and easy for machines to parse and generate. JSON data type is a native data type in SQL Server that allows you to store JSON data and manipulate it using various JSON functions and operators.

JSON data type is implemented as a CLR user-defined data type (UDT) in SQL Server. CLR UDTs are types that are defined in .NET Framework and registered in SQL Server using SQL Server’s CLR integration feature. CLR UDTs can be used like any other native data types in SQL Server and can be stored in tables, variables, and parameters.

JSON data type is supported in SQL Server starting from version 2016 and later versions. In earlier versions of SQL Server, you can still store JSON data as varchar, nvarchar, or text data type but you won’t be able to use JSON functions and operators.

Advantages of JSON Data Type

JSON data type has several advantages over other data types in SQL Server, including:

Limitations of JSON Data Type

JSON data type has some limitations that you should be aware of, including:

Creating a JSON Data Type Column

Creating a JSON data type column is similar to creating any other column in SQL Server. You can create a JSON data type column in a table using the following syntax:

CREATE TABLE table_name (json_column_name JSON [NULL | NOT NULL]);

The JSON data type is defined as JSON [NULL | NOT NULL], where NULL means that the column can have NULL values and NOT NULL means that the column cannot have NULL values.

Inserting JSON Data into a JSON Column

Inserting JSON data into a JSON column is also similar to inserting any other data into a column. You can insert JSON data into a JSON column using the following syntax:

INSERT INTO table_name (json_column_name)VALUES ('{ "name":"John", "age":30, "city":"New York" }');

In this example, we are inserting a simple JSON object that contains three properties: name, age, and city.

Retrieving JSON Data from a JSON Column

Retrieving JSON data from a JSON column is done using the JSON_VALUE function or the JSON_QUERY function. JSON_VALUE function extracts a scalar value from a JSON string or JSON column, whereas JSON_QUERY function extracts a JSON fragment from a JSON string or JSON column.

The following example shows how to retrieve a scalar value from a JSON column:

SELECT JSON_VALUE(json_column_name, '$.name')FROM table_name;

In this example, we are retrieving the value of the name property from the JSON column using the JSON_VALUE function and the ‘$.name’ path expression.

The following example shows how to retrieve a JSON fragment from a JSON column:

SELECT JSON_QUERY(json_column_name, '$.address')FROM table_name;

In this example, we are retrieving the value of the address property from the JSON column using the JSON_QUERY function and the ‘$.address’ path expression.

Manipulating JSON Data

JSON data type provides several functions and operators that allow you to manipulate JSON data easily. In this section, we will cover some of the most commonly used functions and operators.

JSON_VALUE Function

The JSON_VALUE function extracts a scalar value from a JSON string or JSON column. The syntax of the JSON_VALUE function is as follows:

JSON_VALUE(json_string, path_expression)

In this syntax, json_string can be a JSON string or a JSON column in a table, and path_expression is a standard JSON path expression that defines the path to the value you want to extract.

For example, the following JSON_VALUE function extracts the value of the name property from a JSON string:

SELECT JSON_VALUE('{ "name":"John", "age":30, "city":"New York" }', '$.name')AS Name;

In this example, the JSON_VALUE function returns the value ‘John’ as the Name column.

JSON_QUERY Function

The JSON_QUERY function extracts a JSON fragment from a JSON string or JSON column. The syntax of the JSON_QUERY function is as follows:

JSON_QUERY(json_string, path_expression)

In this syntax, json_string can be a JSON string or a JSON column in a table, and path_expression is a standard JSON path expression that defines the path to the fragment you want to extract.

For example, the following JSON_QUERY function extracts the value of the address property from a JSON string:

SELECT JSON_QUERY('{ "name":"John", "age":30, "address":{ "street":"123 Main St", "city":"New York", "state":"NY" } }', '$.address')AS Address;

In this example, the JSON_QUERY function returns the JSON object {“street”:”123 Main St”, “city”:”New York”, “state”:”NY”} as the Address column.

JSON_MODIFY Function

The JSON_MODIFY function modifies a JSON string or JSON column by adding, replacing, or deleting a property or an array element. The syntax of the JSON_MODIFY function is as follows:

JSON_MODIFY(json_string, path_expression, new_value)

In this syntax, json_string can be a JSON string or a JSON column in a table, path_expression is a standard JSON path expression that defines the path to the property or array element you want to modify, and new_value is the new value you want to set.

For example, the following JSON_MODIFY function replaces the value of the age property from 30 to 35:

DECLARE @json NVARCHAR(MAX) = '{ "name":"John", "age":30, "city":"New York" }';SET @json = JSON_MODIFY(@json, '$.age', 35);SELECT @json;

In this example, the JSON_MODIFY function modifies the value of the age property to 35, and returns the modified JSON string: ‘{ “name”:”John”, “age”:35, “city”:”New York” }’.

Frequently Asked Questions

What is the maximum size of a JSON data type in SQL Server?

The maximum size of a JSON data type in SQL Server is 2GB.

Can I create an index on a JSON data type column?

Yes, you can create an index on a JSON data type column using the computed column and persisted computed column feature in SQL Server. However, you cannot create an index on nested properties of a JSON data type column directly.

Can I use JSON data type in stored procedures and functions?

Yes, you can use JSON data type in stored procedures and functions in SQL Server. You can pass JSON data as a parameter to a stored procedure or function, and return JSON data as a result.

Can I use JSON data type in SQL Server Integration Services (SSIS) and Analysis Services (SSAS)?

Yes, you can use JSON data type in SQL Server Integration Services (SSIS) and Analysis Services (SSAS) starting from SQL Server 2016.

Can I convert JSON data to other data types in SQL Server?

Yes, you can convert JSON data to other data types in SQL Server using the CAST or CONVERT function. However, the conversion is limited to scalar values and simple data types like string, integer, and float. Converting complex JSON objects or arrays requires more advanced techniques like JSON functions and operators.

What are some best practices for working with JSON data type in SQL Server?

Some best practices for working with JSON data type in SQL Server include:

• Use JSON data type when you need to store or manipulate structured or semi-structured data that has a flexible schema.
• Avoid using JSON data type when your data has a fixed schema and can be stored more efficiently using traditional SQL data types.
• Use JSON functions and operators instead of string manipulation functions to manipulate JSON data.
• Validate JSON data before storing it in a JSON column.
• Use computed columns and indexes to improve query performance on JSON data type columns.