Hello readers, in this journal article we will explore the topic of querying JSON data in SQL Server. As more and more applications are using JSON to store and transmit data, it is important to know how to efficiently query that data in a database. In this article, we will cover everything from the basics of JSON to advanced querying techniques in SQL Server. We hope you find this article informative and useful. Let’s get started!

What is JSON?

JSON, or JavaScript Object Notation, is a lightweight data interchange format that is easy for humans to read and write and easy for machines to parse and generate. It is based on a subset of the JavaScript Programming Language Standard, but it is language-independent and is supported by many programming languages, including SQL Server.

JSON data consists of key-value pairs, where the keys are strings and the values can be a number, a string, a boolean, an array, or another JSON object. JSON data is often used to store and transmit structured data over the internet.

Storing JSON Data in SQL Server

SQL Server has built-in support for storing JSON data. It provides the JSON data type, which can be used to store JSON data in a table column. When you insert JSON data into a JSON column, SQL Server automatically validates the JSON syntax and stores it in a hierarchy of objects and arrays.

Here is an example of creating a table with a JSON column:

Column Name	Data Type
Id	INT
JsonData	JSON

You can insert JSON data into this table like this:

INSERT INTO MyTable (Id, JsonData)
VALUES (1, '{"name": "John Smith", "age": 30, "email": "john.smith@example.com"}')

Querying JSON Data in SQL Server

Now that we have learned how to store JSON data in SQL Server let’s dive into how we can query this data. SQL Server provides several functions that can be used to query JSON data in a column.

JSON_VALUE

The JSON_VALUE function is used to extract a scalar value from a JSON object. Here is the syntax:

JSON_VALUE (expression, path)

The expression is the JSON object column name, and the path is a string specifying the location of the value to extract. The path can contain properties separated by dots or array indexes enclosed in square brackets.

Here is an example of using JSON_VALUE to extract the name property from the JSON object we inserted earlier:

SELECT JSON_VALUE(JsonData, '$.name') AS Name
FROM MyTable
WHERE Id = 1

This will return:

Name
John Smith

JSON_QUERY

The JSON_QUERY function is used to extract a JSON object or array from a JSON object. Here is the syntax:

JSON_QUERY (expression, path)

The expression is the JSON object column name, and the path is a string specifying the location of the object or array to extract. The path can contain properties separated by dots or array indexes enclosed in square brackets.

Here is an example of using JSON_QUERY to extract the entire JSON object we inserted earlier:

SELECT JSON_QUERY(JsonData, '$') AS Json
FROM MyTable
WHERE Id = 1

This will return:

Json
{ “name”: “John Smith”, “age”: 30, “email”: “john.smith@example.com” }

JSON_MODIFY

The JSON_MODIFY function is used to modify a JSON object or array. Here is the syntax:

JSON_MODIFY (expression, path, newValue)

The expression is the JSON object column name, the path is a string specifying the location of the value to modify, and the newValue is the new value to set. The path can contain properties separated by dots or array indexes enclosed in square brackets.

Here is an example of using JSON_MODIFY to change the email property of the JSON object we inserted earlier:

UPDATE MyTable
SET JsonData = JSON_MODIFY(JsonData, '$.email', 'new.email@example.com')
WHERE Id = 1

Advanced Querying Techniques

Now that we have covered the basics of querying JSON data in SQL Server let’s look at some advanced querying techniques.

Cross Apply

The CROSS APPLY operator in SQL Server can be used to extract values from a JSON array stored in a JSON object column. Here is an example:

SELECT m.Id, a.Value AS Name, a.Age
FROM MyTable m
CROSS APPLY OPENJSON(m.JsonData, '$.employees') 
WITH (Name VARCHAR(100), Age INT) a

In this example, we are extracting the name and age properties from an array of employees stored in the JSON object column. The CROSS APPLY operator joins the table with the results of the OPENJSON function, which converts the JSON array into a set of rows.

Filtered Indexes

SQL Server provides the ability to create filtered indexes, which can be used to index a subset of rows in a table. This can be very useful when you have a large table with a JSON object column and you need to filter on a specific property within the JSON object.

Here is an example of creating a filtered index on the age property of the JSON object column:

CREATE INDEX IX_MyTable_JsonData_Age
ON MyTable (JSON_VALUE(JsonData, '$.age'))
WHERE JSON_VALUE(JsonData, '$.age') IS NOT NULL

This index will only index rows where the age property of the JSON object is not null. This can greatly improve query performance when filtering on the age property.

FAQs

Q: What is the maximum size of JSON data that can be stored in a SQL Server JSON column?

A: The maximum size of a JSON object or array that can be stored in a SQL Server JSON column is 2 GB.

Q: Can I add indexes to JSON columns in SQL Server?

A: Yes, you can add regular or filtered indexes to JSON columns in SQL Server to improve query performance.

Q: Can I use the LIKE operator to search for values in a JSON object?

A: No, you cannot use the LIKE operator to search for values in a JSON object. Instead, you should use the JSON_VALUE or JSON_QUERY functions to extract the value and then use a regular operator to compare the value.

Q: Can I use functions like AVG or SUM on JSON columns in SQL Server?

A: No, you cannot use aggregate functions like AVG or SUM on JSON columns in SQL Server. You must first extract the values using the JSON_VALUE or JSON_QUERY functions and then use the aggregate function on the result.

Q: Can I use JSON data in SQL Server stored procedures?

A: Yes, you can use JSON data in SQL Server stored procedures. You can pass JSON data as a parameter to a stored procedure, or you can return JSON data from a stored procedure using the FOR JSON clause.

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