Als u JSON_VALUE() . gebruikt om waarden te retourneren die uit een lange tekenreeks bestaan, kan het zijn dat het NULL . retourneert in plaats van de werkelijke waarde.
Of misschien krijgt u een foutmelding.
De oorzaak
Dit probleem treedt op omdat JSON_VALUE() retourneert een enkele tekstwaarde van het type nvarchar(4000) .
Bij gebruik van JSON_VALUE() om strings te retourneren die langer zijn dan 4000 tekens, krijg je een foutmelding of een NULL waarde, afhankelijk van de padmodus die u gebruikt.
Lax-modus versus strikte modus
Of je nu een foutmelding krijgt of NULL hangt af van of u lax . gebruikt of strict modus.
Wanneer de waarde groter is dan 4000 tekens:
- In
laxmodus,JSON_VALUE()geeft nul terug. - In
strictmodus,JSON_VALUE()geeft een fout terug.
Voorbeeld van het probleem
Hier is een voorbeeld van code die het probleem veroorzaakt.
Laten we twee voorbeelden doen; een in lax modus, en de andere in strict modus.
Lax-modus
DECLARE @json nvarchar(max) = N'{
"article" : {
"id" : 1,
"text" : "If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error."
}
}';
SELECT JSON_VALUE(@json, 'lax $.article.text');Resultaat:
+--------------------+ | (No column name) | |--------------------| | NULL | +--------------------+
Zoals vermeld, in lax modus retourneert het NULL .
Strikte modus
DECLARE @json nvarchar(max) = N'{
"article" : {
"id" : 1,
"text" : "If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error."
}
}';
SELECT JSON_VALUE(@json, 'strict $.article.text');Resultaat:
Msg 13625, Level 16, State 1, Line 7 String value in the specified JSON path would be truncated.
Zoals verwacht krijgen we een foutmelding. Gelukkig geeft de fout een idee van wat er mis is gegaan, aangezien er wordt vermeld dat de tekenreekswaarde zou worden afgekapt.
Oplossing
Gelukkig is de OPENJSON() functie heeft niet dezelfde beperking van 4000 tekens die JSON_VALUE() heeft op zijn retourwaarde.
OPENJSON() geeft JSON-waarden terug als een nvarchar(max) .
Daarom kunnen we de volgende code gebruiken om het probleem op te lossen.
DECLARE @json nvarchar(max) = N'{
"article" : {
"id" : 1,
"text" : "If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error."
}
}';
SELECT text FROM OPENJSON(@json, '$.article')
WITH (text nvarchar(max) '$.text');Resultaat:
If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error. If you have to return scalar values greater than 4000 characters, use the OPENJSON function instead of JSON_VALUE. This text contains more than 4000 characters, which will cause issues for the JSON_VALUE function in SQL Server. This is because the JSON_VALUE function returns a single text value of type nvarchar(4000). If the value is greater than 4000 characters: In lax mode, JSON_VALUE returns null. In strict mode, JSON_VALUE returns an error.