JSON Path Expressions (SQL Server)

Artikkeli
02/12/2024

Applies to: SQL Server 2016 (13.x) and later Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics (serverless SQL pool only)

Use JSON path expressions to reference the properties of JSON objects.

You have to provide a path expression when you call the following functions.

When you call OPENJSON to create a relational view of JSON data. For more info, see OPENJSON (Transact-SQL).
When you call JSON_VALUE to extract a value from JSON text. For more info, see JSON_VALUE (Transact-SQL).
When you call JSON_QUERY to extract a JSON object or an array. For more info, see JSON_QUERY (Transact-SQL).
When you call JSON_MODIFY to update the value of a property in a JSON string. For more info, see JSON_MODIFY (Transact-SQL).

Parts of a path expression

A path expression has two components.

The optional path mode, with a value of lax or strict.
The path itself.

Path mode

At the beginning of the path expression, optionally declare the path mode by specifying the keyword lax or strict. The default is lax.

In lax mode, the function returns empty values if the path expression contains an error. For example, if you request the value $.name, and the JSON text doesn't contain a name key, the function returns null, but does not raise an error.
In strict mode, the function raises an error if the path expression contains an error.

The following query explicitly specifies lax mode in the path expression.

DECLARE @json NVARCHAR(MAX);
SET @json=N'{ ... }';

SELECT * FROM OPENJSON(@json, N'lax $.info');

Path

After the optional path mode declaration, specify the path itself.

The dollar sign ($) represents the context item.
The property path is a set of path steps. Path steps can contain the following elements and operators.
- Key names. For example, $.name and $."first name". If the key name starts with a dollar sign or contains special characters such as spaces or dot operators(.), surround it with quotes.
- Array elements. For example, $.product[3]. Arrays are zero-based.
- The dot operator (.) indicates a member of an object. For example, in $.people[1].surname, surname is a child of people.

Examples

The examples in this section reference the following JSON text.

{
    "people": [{
        "name": "John",
        "surname": "Doe"
    }, {
        "name": "Jane",
        "surname": null,
        "active": true
    }]
}

The following table shows some examples of path expressions.

Path expression	Value
$.people[0].name	John
$.people[1]	{ "name": "Jane", "surname": null, "active": true }
$.people[1].surname	null
$	{ "people": [ { "name": "John", "surname": "Doe" }, { "name": "Jane", "surname": null, "active": true } ] }

How built-in functions handle duplicate paths

If the JSON text contains duplicate properties - for example, two keys with the same name on the same level - the JSON_VALUE and JSON_QUERY functions return only the first value that matches the path. To parse a JSON object that contains duplicate keys and return all values, use OPENJSON, as shown in the following example.

DECLARE @json NVARCHAR(MAX);
SET @json=N'{"person":{"info":{"name":"John", "name":"Jack"}}}';

SELECT value
  FROM OPENJSON(@json,'$.person.info');

Learn more about JSON in SQL Server and Azure SQL Database

Microsoft videos

Note

Some of the video links in this section may not work at this time. Microsoft is migrating content formerly on Channel 9 to a new platform. We will update the links as the videos are migrated to the new platform.

For a visual introduction to the built-in JSON support in SQL Server and Azure SQL Database, see the following videos:

JSON as a bridge between NoSQL and relational worlds

Jaa