Mastering OPENJSON and JSON_VALUE: A Comprehensive Guide for Selecting Rows with Dynamic Keys

Introduction to OPENJSON and Dynamic Key Selection

SQL Server provides a powerful feature called OPENJSON() that allows us to parse JSON data directly from our database tables. This feature has become increasingly popular in recent years, especially with the advent of NoSQL databases and big data storage solutions. However, one common challenge when working with JSON data is selecting specific rows based on dynamic keys.

In this article, we’ll explore a solution using a combination of OPENJSON() and JSON_VALUE(). We’ll break down the technical details, provide examples, and cover best practices for implementing this approach in your own SQL Server applications.

Understanding OPENJSON()

OPENJSON() is a table-valued function that takes an XML or JSON column as input and returns a result set containing individual JSON objects. This function allows us to easily query and manipulate JSON data within our database tables.

Here’s an example of how OPENJSON() works:

CREATE TABLE JsonTable (
    Id INT,
    Data NVARCHAR(MAX)
)

INSERT INTO JsonTable (Id, Data) VALUES (1, '[{"status":0,"approval":"0","entrydate":"2023-01-30"},{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"}]')

SELECT *
FROM OPENJSON(JsonTable.Data)
CROSS APPLY (
    SELECT [value]
    FROM JSON_VALUE([value], '$.status')
) ASJV

This example shows how we can use OPENJSON() to parse the JSON data in our table and select individual rows using a CROSS APPLY query.

Using JSON_VALUE() with OPENJSON()

As mentioned earlier, one common challenge when working with dynamic keys is selecting specific rows based on those keys. This is where JSON_VALUE() comes into play.

JSON_VALUE() is a function that extracts the value of a specified JSON path from a given JSON document. We can use this function to retrieve the value of our dynamic key and then compare it against a predetermined value.

Here’s an updated example that demonstrates how we can use JSON_VALUE() with OPENJSON():

CREATE TABLE JsonTable (
    Id INT,
    Data NVARCHAR(MAX)
)

INSERT INTO JsonTable (Id, Data) VALUES 
(1, '[{"30":{"status":0,"approval":"0","entrydate":"2023-01-30"}},{"26":{"status":0,"approval":"0","entrydate":"2023-01-30"}}]'),
(2, '[{"12":{"status":0,"approval":"0","entrydate":"2023-01-30"},{"13":{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"}}]'),
(3, '[{"20":{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"},{"24":{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"}}]')

SELECT *
FROM JsonTable
WHERE EXISTS (
    SELECT 1
    FROM OPENJSON(JsonTable.Data)
    WHERE JSON_VALUE([value], '$.key') = '0'
)

In this example, we’re using JSON_VALUE() to extract the value of our dynamic key ($.key) from each row in the table. We then compare that value against '0' to select rows where the value is equal to '0'.

Using OPENJSON and JSON_VALUE with Dynamic Keys

Now that we’ve explored how to use OPENJSON() and JSON_VALUE(), let’s dive deeper into using these functions together to select rows based on dynamic keys.

One common approach when working with dynamic keys is to use a combination of OPENJSON() and JSON_VALUE() within a WHERE clause. This allows us to dynamically compare the value of our key against a predetermined value.

Here’s an updated example that demonstrates how we can use OPENJSON() and JSON_VALUE() together:

CREATE TABLE JsonTable (
    Id INT,
    Data NVARCHAR(MAX)
)

INSERT INTO JsonTable (Id, Data) VALUES 
(1, '[{"30":{"status":0,"approval":"0","entrydate":"2023-01-30"},{"26":{"status":0,"approval":"0","entrydate":"2023-01-30"}}]'),
(2, '[{"12":{"status":0,"approval":"0","entrydate":"2023-01-30"},{"13":{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"}}]'),
(3, '[{"20":{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"},{"24":{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"}}]')

SELECT *
FROM JsonTable
WHERE EXISTS (
    SELECT 1
    FROM OPENJSON(JsonTable.Data)
    WHERE JSON_VALUE([value], '$.key') = '0'
)

In this example, we’re using OPENJSON() to parse the JSON data in our table and selecting rows where the value of our dynamic key ($.key) is equal to '0'.

Using OPENJSON and JSON_VALUE with Multiple Dynamic Keys

What if you have multiple dynamic keys that need to be compared against specific values? This is where things can get a bit more complex, but we can still use OPENJSON() and JSON_VALUE() together to achieve the desired result.

One common approach when working with multiple dynamic keys is to use nested JSON paths within our WHERE clause. Here’s an updated example that demonstrates how we can use OPENJSON() and JSON_VALUE() together:

CREATE TABLE JsonTable (
    Id INT,
    Data NVARCHAR(MAX)
)

INSERT INTO JsonTable (Id, Data) VALUES 
(1, '[{"30":{"status":0,"approval":"0","entrydate":"2023-01-30"},{"26":{"status":0,"approval":"0","entrydate":"2023-01-30"}}]'),
(2, '[{"12":{"status":0,"approval":"0","entrydate":"2023-01-30"},{"13":{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"}}]'),
(3, '[{"20":{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"},{"24":{"status":1,"approval":"20022-xxxx","entrydate":"2023-01-30"}}]')

SELECT *
FROM JsonTable
WHERE EXISTS (
    SELECT 1
    FROM OPENJSON(JsonTable.Data)
    WHERE JSON_VALUE([value], '$.key1') = '0' AND JSON_VALUE([value], '$.key2') = '20022-xxxx'
)

In this example, we’re using OPENJSON() to parse the JSON data in our table and selecting rows where the value of two dynamic keys ($.key1 and $.key2) match against specific values.

Best Practices for Using OPENJSON and JSON_VALUE

When working with OPENJSON() and JSON_VALUE(), there are a few best practices to keep in mind:

Use meaningful table aliases when referencing the result set returned by OPENJSON(). This makes it easier to understand your code.
Avoid using subqueries within your WHERE clause. Instead, use CROSS APPLY or JOIN to join with the result set returned by OPENJSON().
Be careful when using nested JSON paths within your WHERE clause. Make sure you’re referencing the correct nodes in your JSON data.

Conclusion

OPENJSON() and JSON_VALUE() are powerful functions in SQL Server that allow us to easily query and manipulate JSON data within our database tables. By combining these functions with dynamic keys, we can select rows based on specific values.

Remember to use meaningful table aliases when referencing the result set returned by OPENJSON(), avoid subqueries within your WHERE clause, and be careful when using nested JSON paths.

With practice and patience, you’ll become proficient in using OPENJSON() and JSON_VALUE() together to achieve complex query results.

Last modified on 2024-05-20