Om du använder JSON_VALUE() för att returnera värden som består av en lång sträng kan du upptäcka att den returnerar NULL istället för det faktiska värdet.
Eller så kanske du får ett felmeddelande.
Orsaken
Det här problemet uppstår eftersom JSON_VALUE() returnerar ett enda textvärde av typen nvarchar(4000) .
När du använder JSON_VALUE() för att returnera strängar som är längre än 4000 tecken får du antingen ett felmeddelande eller en NULL värde, beroende på vilket sökvägsläge du använder.
Laxläge vs strikt läge
Oavsett om du får ett felmeddelande eller NULL kommer att bero på om du använder lax eller strict läge.
När värdet är större än 4000 tecken:
- I
laxläge,JSON_VALUE()returnerar null. - I
strictläge,JSON_VALUE()returnerar ett fel.
Exempel på problemet
Här är ett exempel på kod som orsakar problemet.
Låt oss ta två exempel; en i lax läge och den andra i strict läge.
Laxläge
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');Resultat:
+--------------------+ | (No column name) | |--------------------| | NULL | +--------------------+
Som nämnts i lax läge returnerar den NULL .
Strikt läge
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');Resultat:
Msg 13625, Level 16, State 1, Line 7 String value in the specified JSON path would be truncated.
Som väntat får vi ett fel. Lyckligtvis ger felet en ledtråd om vad som gick fel, eftersom det nämner att strängvärdet skulle trunkeras.
Lösning
Lyckligtvis är OPENJSON() Funktionen har inte samma begränsning på 4000 tecken som JSON_VALUE() har på sitt returvärde.
OPENJSON() returnerar JSON-värden som en nvarchar(max) .
Därför kan vi använda följande kod för att lösa problemet.
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');Resultat:
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.