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ISJSON (Transact-SQL)

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Applies to: SQL Server 2016 (13.x) and later Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics SQL analytics endpoint in Microsoft Fabric Warehouse in Microsoft Fabric

Tests whether a string contains valid JSON.

Transact-SQL syntax conventions

Syntax

ISJSON ( expression [, json_type_constraint] )

Arguments

expression

The string to test.

json_type_constraint

Specifies the JSON type to check in the input. Valid values are VALUE, ARRAY, OBJECT, or SCALAR. Introduced in SQL Server 2022 (16.x).

Note

The argument json_type_constraint is not supported in Azure Synapse Analytics Dedicated pools

Return value

Returns 1 if the string contains valid JSON; otherwise, returns 0. Returns NULL if expression is null.

If the statement omits json_type_constraint, the function tests if the input is a valid JSON object or array and returns 1 otherwise, it returns 0.

If the json_type_constraint is specified then the function checks for the JSON type as follows:

Value Description
VALUE Tests for a valid JSON value. This can be a JSON object, array, number, string or one of the three literal values (false, true, null)
ARRAY Tests for a valid JSON array
OBJECT Tests for a valid JSON object
SCALAR Tests for a valid JSON scalar – number or string

The json_type_constraint value SCALAR can be used to test for IETF RFC 8259 conformant JSON document that contains only a JSON scalar value at top level. A JSON document that doesn't contain a JSON scalar value at top level conforms with IETF RFC 4627.

Does not return errors.

Remarks

ISJSON does not check the uniqueness of keys at the same level.

Examples

Example 1

The following example runs a statement block conditionally if the parameter value @param contains valid JSON.

DECLARE @param <data type>
SET @param = <value>

IF (ISJSON(@param) > 0)  
BEGIN  
     -- Do something with the valid JSON value of @param.  
END

Example 2

The following example returns rows in which the column json_col contains valid JSON.

SELECT id, json_col
FROM tab1
WHERE ISJSON(json_col) = 1

Example 3

The following example returns rows in which the column json_col contains valid JSON SCALAR value at top level.

SELECT id, json_col
FROM tab1
WHERE ISJSON(json_col, SCALAR) = 1

Example 4

The following example returns 1 since the input is a valid JSON value - true.

SELECT ISJSON('true', VALUE)

Example 5

The following example returns 0 since the input is an invalid JSON value.

SELECT ISJSON('test string', VALUE)

Example 6

The following example returns 1 since the input is a valid JSON scalar according to RFC 8259.

SELECT ISJSON('"test string"', SCALAR)

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