OPENJSON and CROSS APPLY

OPENJSON is pretty central to manipulating JSON documents in T-SQL.

As we’ve seen, we can use a default schema that will return metadata about the JSON document or we can use an explicit schema where we supply a WITH clause and a PATH to the data that we want.

So far, in our examples we have either used the default schema or an explicit schema – but we have not mixed the two.

Indeed if you try this in a simple query you’ll find it is not possible without the use of APPLY operator.

OPENJSON is actually a table-valued function that parses JSON – either into an explicit schema (that we provide) or the default schema.

We can mix both the default and explicit schema by using CROSS APPLY

Like so

DECLARE @json NVARCHAR(MAX) =
N'
{
    "Configuration Property": {
      "Configuration name": "recovery interval (min)",
      "Value": 0,
      "minimum": 0,
      "maximum": 32767,
      "value_in_use": 0,
      "description": "Maximum recovery interval in minutes",
      "is_dynamic": true,
      "is_advanced": true
    }
}
';
 
SELECT 
	 DS.[key]
	,DS.[value]
	,DS.[type]
	,ES.[Configuration name]
	,ES.[Value]
	,ES.[minimum]
	,ES.[maximum]
	,ES.[value_in_use]
	,ES.[description]
	,ES.[is_dynamic]
	,ES.[is_advanced] 
FROM  
     OPENJSON(@json)  AS DS
CROSS APPLY
     OPENJSON(DS.[value])
WITH
(
	 [Configuration name]  NVARCHAR(35)
	,[Value]               NVARCHAR(35)
	,[minimum]             NVARCHAR(35)
	,[maximum]             NVARCHAR(35)
	,[value_in_use]        NVARCHAR(35)
	,[description]         NVARCHAR(35)
	,[is_dynamic]          NVARCHAR(35)
	,[is_advanced]         NVARCHAR(35)
) AS ES
GO

This technique can come in extremely handy when attempting to drill down into sub arrays and objects contained in a JSON document.

Notice also that different aliasing (of the default and explicit schema) has allowed us to request data from both the default schema and the explicit schema. This has enabled us to get to the element that is named value – as this name appears in both the default and explicit schema names and thus requires an alias.

I hope this has helped on your SQL Server JSON journey. We’ll see more real soon.

Have a great day

Cheers

Marty

OPENJSON : Getting to the data, and the PATH – PART I

Recently we reviewed FOR JSON PATH. That was used for shaping tabular data (data that comes directly from a SQL table) into a JSON document.

The PATH we are talking about here is used with OPENJSON to get to the data that is contained in the JSON document.

We’ve seen an example of OPENJSON and reading data with an explicit schema.

SELECT
     [configuration_id]
    ,[Configuration name] 
    ,[Value]          = TRY_CONVERT(sql_variant  , [Value]) 
    ,[minimum]        = TRY_CONVERT(sql_variant  , [minimum]) 
    ,[maximum]        = TRY_CONVERT(sql_variant  , [maximum]) 
    ,[value_in_use]   = TRY_CONVERT(sql_variant  , [value_in_use]) 
    ,[description]    = TRY_CONVERT(sql_variant  , [description]) 
    ,[is_dynamic]
    ,[is_advanced]
FROM
    OPENJSON
(
'
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
'
)
WITH
(
     [configuration_id]     INT 
    ,[Configuration name]   NVARCHAR(35)
    ,[Value]                NVARCHAR(200)
    ,[minimum]              NVARCHAR(200)
    ,[maximum]              NVARCHAR(200)
    ,[value_in_use]         NVARCHAR(200)
    ,[description]          NVARCHAR(200)
    ,[is_dynamic]           BIT
    ,[is_advanced]          BIT
);
GO

Turns out that in this example, the data is right at the top level of the document.

 {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }

and so we didn’t need to explicitly state the PATH – however we still could have. And here it is.

SELECT
     [configuration_id]
    ,[Configuration name] 
    ,[Value]          = TRY_CONVERT(sql_variant  , [Value]) 
    ,[minimum]        = TRY_CONVERT(sql_variant  , [minimum]) 
    ,[maximum]        = TRY_CONVERT(sql_variant  , [maximum]) 
    ,[value_in_use]   = TRY_CONVERT(sql_variant  , [value_in_use]) 
    ,[description]    = TRY_CONVERT(sql_variant  , [description]) 
    ,[is_dynamic]
    ,[is_advanced]
FROM
    OPENJSON
(
'
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
'
, '$')
WITH
(
     [configuration_id]     INT 
    ,[Configuration name]   NVARCHAR(35)
    ,[Value]                NVARCHAR(200)
    ,[minimum]              NVARCHAR(200)
    ,[maximum]              NVARCHAR(200)
    ,[value_in_use]         NVARCHAR(200)
    ,[description]          NVARCHAR(200)
    ,[is_dynamic]           BIT
    ,[is_advanced]          BIT
);
GO

The query below has the PATH defined explicitly in the WITH clause.

SELECT
     [configuration_id]
    ,[Configuration name] 
    ,[Value]          = TRY_CONVERT(sql_variant  , [Value]) 
    ,[minimum]        = TRY_CONVERT(sql_variant  , [minimum]) 
    ,[maximum]        = TRY_CONVERT(sql_variant  , [maximum]) 
    ,[value_in_use]   = TRY_CONVERT(sql_variant  , [value_in_use]) 
    ,[description]    = TRY_CONVERT(sql_variant  , [description]) 
    ,[is_dynamic]
    ,[is_advanced]
FROM
    OPENJSON
(
'
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
')
WITH
(
     [configuration_id]     INT               '$.configuration_id'
    ,[Configuration name]   NVARCHAR(35)      '$."Configuration name"'
    ,[Value]                NVARCHAR(200)     '$.Value'
    ,[minimum]              NVARCHAR(200)     '$.minimum'
    ,[maximum]              NVARCHAR(200)     '$.maximum'
    ,[value_in_use]         NVARCHAR(200)     '$.value_in_use'
    ,[description]          NVARCHAR(200)     '$.description'
    ,[is_dynamic]           BIT               '$.is_dynamic'
    ,[is_advanced]          BIT               '$.is_advanced'
);
GO

Notice also that Configuration name has a space in it. So, in the PATH we simply enclose it in double quotes “..” – in a similar way to how square brackets would be used in a T-SQL expression.

Lets, look at a slightly different shaped JSON document and see how we would change the PATH in the WITH clause to locate all of the desired values.

SELECT 
	 [configuration_id]
    ,[Configuration name] 
    ,[Value]          = TRY_CONVERT(sql_variant  , [Value]) 
    ,[minimum]        = TRY_CONVERT(sql_variant  , [minimum]) 
    ,[maximum]        = TRY_CONVERT(sql_variant  , [maximum]) 
    ,[value_in_use]   = TRY_CONVERT(sql_variant  , [value_in_use]) 
    ,[description]    = TRY_CONVERT(sql_variant  , [description]) 
    ,[is_dynamic]
    ,[is_advanced]
FROM
	OPENJSON(
'
{
  "configuration_id": 101,
  "Configuration_Property": {
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
}
')
WITH
(
     [configuration_id]     INT            '$."configuration_id"'
    ,[Configuration name]   NVARCHAR(35)   '$."Configuration_Property"."Configuration name"'
    ,[Value]                NVARCHAR(200)  '$."Configuration_Property"."Value"'
    ,[minimum]              NVARCHAR(200)  '$."Configuration_Property"."minimum"'
    ,[maximum]              NVARCHAR(200)  '$."Configuration_Property"."maximum"'
    ,[value_in_use]         NVARCHAR(200)  '$."Configuration_Property"."value_in_use"'
    ,[description]          NVARCHAR(200)  '$."Configuration_Property"."description"'
    ,[is_dynamic]           BIT            '$."Configuration_Property"."is_dynamic"'
    ,[is_advanced]          BIT            '$."Configuration_Property"."is_advanced"'	
);

Notice, that no ‘default path’ is specified on the OPENJSON clause (after the document on line 27).

I hope this has helped on your SQL Server JSON journey. We’ll see more real soon.

Have a great day

Cheers

Marty

Download Files

OPENJSON, explicit schema and data type

Back in our last instalment, we looked at OPENJSON and how we can get data into a tabular format from a JSON document.

Readers may have noticed that we used data from the sys.configurations table in order to generate the JSON document.

However, when we read the data from the document into tabular format we specified that the columns

  • Value
  • minimum
  • maximum
  • value_in_use
  • description

Which are of type SQL_VARIANT in the table were actually of type NVARCHAR(200) in the resultset that was brought back from the JSON document.

SELECT
     [configuration_id]
    ,[Configuration name] 
    ,[Value]
    ,[minimum] 
    ,[maximum]
    ,[value_in_use]
    ,[description]
    ,[is_dynamic]
    ,[is_advanced]
FROM
	OPENJSON
(
'
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
'
)
WITH
(
     [configuration_id]     INT 
    ,[Configuration name]   NVARCHAR(35)
    ,[Value]                NVARCHAR(200)
    ,[minimum]              NVARCHAR(200)
    ,[maximum]              NVARCHAR(200)
    ,[value_in_use]         NVARCHAR(200)
    ,[description]          NVARCHAR(200)
    ,[is_dynamic]           BIT
    ,[is_advanced]          BIT
);
GO

So, why was that? and can we fix it?

Well, JSON and has a handful of data types and SQL Server has lots. So there’s not a one-to-one match.

The best thing to do would be to being them back as one of the simple types (likely NVARCHAR()) and then CAST them in the SELECT to the actual desired data type.

Like so

SELECT
     [configuration_id]
    ,[Configuration name] 
    ,[Value]          = TRY_CONVERT(sql_variant  , [Value]) 
    ,[minimum]        = TRY_CONVERT(sql_variant  , [minimum]) 
    ,[maximum]        = TRY_CONVERT(sql_variant  , [maximum]) 
    ,[value_in_use]   = TRY_CONVERT(sql_variant  , [value_in_use]) 
    ,[description]    = TRY_CONVERT(sql_variant  , [description]) 
    ,[is_dynamic]
    ,[is_advanced]
FROM
	OPENJSON
(
'
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
'
)
WITH
(
     [configuration_id]     INT 
    ,[Configuration name]   NVARCHAR(35)
    ,[Value]                NVARCHAR(200)
    ,[minimum]              NVARCHAR(200)
    ,[maximum]              NVARCHAR(200)
    ,[value_in_use]         NVARCHAR(200)
    ,[description]          NVARCHAR(200)
    ,[is_dynamic]           BIT
    ,[is_advanced]          BIT
);
GO

The result set looks the same, however if the values returned are now of the correct data type. So if you wanted to do anything with the resultset like joining on the original table then you would not see any implicit casting.

So, that’s just a small tip of how to handle data type differences between SQL Server and JSON.

I hope this has helped on your SQL Server JSON journey. We’ll see more real soon.

Have a great day

Cheers

Marty

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OPENJSON, explicit schema and data type

OPENJSON – using an explicit schema. The WITH clause.

G’day,

Previously, we have looked at using OPENJSON to gain knowledge about the JSON document that we have presented to the function.

A bit like this

SELECT
	*
FROM
	OPENJSON
(
'
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
'
)
Columns returned using OPENJSON with the default schema
Columns returned using OPENJSON with the default schema

Notice that we didn’t request any columns in the SELECT statement, but we got three columns back

  • Key
  • value
  • type

That’s great metadata information – but what if we wanted the actual values from the JSON.

Well, the statement above used OPENJSON with the default schema – which is basically no column list defined. If we want to define a list then we need to use a WITH clause that defines an EXPLICIT schema – like so

SELECT
	 *
FROM
	OPENJSON
(
'
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
'
)
WITH
(
     [configuration_id]     INT 
    ,[Configuration name]   NVARCHAR(35)
    ,[Value]                NVARCHAR(200)
    ,[minimum]              NVARCHAR(200)
    ,[maximum]              NVARCHAR(200)
    ,[value_in_use]         NVARCHAR(200)
    ,[description]          NVARCHAR(200)
    ,[is_dynamic]           BIT
    ,[is_advanced]          BIT
);
GO
Values returned when supply a explicit list to OPENJSON
Values returned when supply a explicit list to OPENJSON

You might also notice that the names in the WITH clause match those in the JSON document – We can also add these as a column list to the SELECT statement, rather than using SELECT *

Notice also that if we ask for a value in the WITH clause that does not appear in the JSON document (maybe because of a typo) then we simply get a NULL returned in the SELECT list.

Notice here that the name of the first column is incorrect. So we get a null in the resultset.

SELECT
	*
FROM
	OPENJSON
(
'
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
'
)
WITH
(
     [configuration_if]     INT 
    ,[Configuration name]   NVARCHAR(35)
    ,[Value]                NVARCHAR(200)
    ,[minimum]              NVARCHAR(200)
    ,[maximum]              NVARCHAR(200)
    ,[value_in_use]         NVARCHAR(200)
    ,[description]          NVARCHAR(200)
    ,[is_dynamic]           BIT
    ,[is_advanced]          BIT
);
GO
A value in the explicit OPENJSON list that is not actually in the JSON

This is perhaps one reason that we should include an explicit column list in the SELECT statement

SELECT
     [configuration_id]
    ,[Configuration name] 
    ,[Value] 
    ,[minimum]
    ,[maximum] 
    ,[value_in_use]
    ,[description]
    ,[is_dynamic]
    ,[is_advanced]
FROM
	OPENJSON
(
'
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
'
)
WITH
(
     [configuration_id]     INT 
    ,[Configuration name]   NVARCHAR(35)
    ,[Value]                NVARCHAR(200)
    ,[minimum]              NVARCHAR(200)
    ,[maximum]              NVARCHAR(200)
    ,[value_in_use]         NVARCHAR(200)
    ,[description]          NVARCHAR(200)
    ,[is_dynamic]           BIT
    ,[is_advanced]          BIT
);
GO

And we pretty much see exactly what we had before.

Both explicit OPENJSON schema fully defined along with SELECT column list
Both explicit OPENJSON schema fully defined along with SELECT column list

Next up is some more useful tips about OPENJSON

Have a great day

Cheers

Marty

Download Files

OPENJSON – using an explicit schema. The WITH clause

T-SQL Sequences and the OVER() clause

Using a SEQUENCE object – in unusual ways!

If you’ve delved into Window Functions at all then you probably have read the documentation about the OVER() clause.

While reading this recently, I noticed that a sequence can have an OVER() clause attached to it.

I was curious about this so I experimented.

Consider the following.

USE tempdb;
GO
IF EXISTS(SELECT * FROM sys.sequences AS S WHERE S.[name] = 'TestSeq' AND OBJECT_SCHEMA_NAME(S.[object_id]) = 'dbo')
    BEGIN
        DROP SEQUENCE dbo.TestSeq;
    END;
GO
CREATE sequence dbo.TestSeq
AS  
    BIGINT
    START WITH 1
    INCREMENT BY 1
    NO CYCLE
    NO CACHE;
GO

So now we have a SEQUENCE object that we can play with.

And, as expected the following worked fine.

SELECT NEXT VALUE FOR dbo.TestSeq;
/*
Lets put the value into a variable
*/
DECLARE @value BIGINT = 0;
SELECT @value =NEXT VALUE FOR dbo.TestSeq;

But, did you also know that you can do this (whether or not you would want to is a different matter)

SELECT NEXT VALUE FOR dbo.TestSeq AS [TestValue];
SELECT NEXT VALUE FOR dbo.TestSeq OVER(ORDER BY NEWID()) AS [TestValue];
SELECT NEXT VALUE FOR dbo.TestSeq OVER(ORDER BY (SELECT NULL));
SELECT NEXT VALUE FOR dbo.TestSeq OVER(ORDER BY (SELECT 1));
SELECT NEXT VALUE FOR dbo.TestSeq OVER(ORDER BY RAND());

That’s pretty interesting, but not a whole load of use.

We can also do this

USE tempdb;
GO
/*
There's three of these objects in tempdb
*/
SELECT 
	RowNumber = NEXT VALUE FOR dbo.TestSeq OVER(ORDER BY O.[type] ASC)
	,* 
FROM 
	sys.objects AS O
WHERE
	O.[type] IN ('SQ')
ORDER BY
	RowNumber DESC;
/*
And ordered the opposite way around
*/
SELECT 
	RowNumber = NEXT VALUE FOR dbo.TestSeq OVER(ORDER BY O.[type] DESC)
	,* 
FROM 
	sys.objects AS O
WHERE
	O.[type] IN ('SQ')
ORDER BY
	RowNumber ASC;

Did you spot that a column from sys.objects was used in the OVER() clause and that the ORDER BY in the OVER() clause and main query are the opposite away around.

We are unable to use PARTITION within the OVER() clause of a SEQUENCE, which total makes sense as we only get one row back.

This could come in handy and save us a join.

I hope that helps somebody out someday.

Have a great day

Cheers

Marty.

Download the code (Azure Data Studio notebook)

Concatenating Strings, NULLs and EXEC

G’day,

SQL Server’s great – its been teaching me a lot for many years. But every so often you get a surprise. Sometimes it’s a nice one, sometimes it more of the ‘really, are you sure kind’ – and then you realise, yes SQL Server – you’re correct, I really should have known that.

This one involved

  • A cursor
  • String concatenation
  • Executing a T-SQL Statement

The first two of these didn’t suprise me – after I’d thought about it.

The last one did

I’ll attempt to give an example of what occured

I have a table

USE tempdb;
GO

IF OBJECT_ID('dbo.Issue') IS NOT NULL
	BEGIN
		DROP TABLE dbo.Issue
	END;


CREATE TABLE dbo.Issue
(
	SomeName NVARCHAR(50) NULL
);

and, we’re inserting into that table using a concatenated T-SQL string, like so

DECLARE @InsertValue NVARCHAR(50) = N'TestValue';
DECLARE @SQL NVARCHAR(500) = 'INSERT INTO dbo.Issue(SomeName) VALUES(''' + @InsertValue + ''');';
PRINT @SQL;
EXEC(@SQL);

As you’d expect one row goes in

However, the issue that I saw arose when the variable being INSERTed was NULL, like so

DECLARE @InsertValue NVARCHAR(50) = NULL;
DECLARE @SQL NVARCHAR(500) = 'INSERT INTO dbo.Issue(SomeName) VALUES(''' + @InsertValue + ''');';
PRINT @SQL;
EXEC(@SQL);

You’ll notice (if you run the code) that nothing gets printed – which is fair enough as a NULL in a string concatenation will unltimatly yeild a NULL, as anything + an unknown (NULL) is an unknown (NULL)

That wasn’t the surprising part – although it did get me to think a bit at first.

The surprising part (to me at least), was that the string – which is now NULL -has been run inside the EXEC(..) call, had not errored, had not failed, but had not inserted anything either

Try it

DECLARE @InsertValue NVARCHAR(50) = NULL;
DECLARE @SQL NVARCHAR(500) = 'INSERT INTO dbo.Issue(SomeName) VALUES(''' + @InsertValue + ''');';
PRINT @SQL;
EXEC(@SQL);
SELECT * FROM dbo.Issue;

You can try this more simply by executing a NULL string

DECLARE @Test NVARCHAR(20) = NULL;
EXEC(@Test);

Note however, that you can’t directly execute a NULL (although why you’d want to is a different matter 🙂 )

EXEC(NULL)
Msg 156, Level 15, State 1, Line 44
Incorrect syntax near the keyword 'NULL'.

So, now you know.

If you’ve never seen this before (or even if you have, but a long time ago) then this could easily make you wonder what is going on.

I hope this helps somebody.

Have a great day.

Cheers

Martin.

JSON data and a T-SQL variable.

G’day,

You may have noticed when looking at FOR JSON AUTO or FOR JSON PATH that both clauses result in one single column that contains a JSON string.

USE tempdb;
GO

SELECT 
	*
FROM
	sys.configurations AS C
ORDER BY
	C.[configuration_id]
FOR JSON AUTO;
/*
Or
*/
SELECT 
	*
FROM
	sys.configurations AS C
ORDER BY
	C.[configuration_id]
FOR JSON PATH;

But, what if we wanted this data to be put directly into a T-SQL variable?

For a standard T-SQL Statement, we might use something of the form

DECLARE @ConfigurationName SYSNAME = N'';
SELECT 
	@ConfigurationName = C.[name]
FROM	
	sys.configurations AS C
WHERE
	C.configuration_id = 101;
PRINT @ConfigurationName;

The WHERE clause in the above statement ensures that only one row is brought back for [name] and everything is fine.

As an aside, consider what would happen in the above statement if we omitted the WHERE clause (and it brought back multiple rows of data)

Yes, we’d bring back more than a single value, but would we expect to get an error?

Try it

DECLARE @ConfigurationName SYSNAME = N'';
SELECT 
	@ConfigurationName = C.[name]
FROM	
	sys.configurations AS C
PRINT @ConfigurationName;

Notice that this time we get the last value in the returned list of names. On my system that is ‘allow polybase export’ and not ‘recovery interval (min)’ as in the initial example when we had a WHERE clause.

The lesson here is if you expect a single value then ensure that you are only getting a single value back.

But that is a different discussion for a different day.

Right now back to JSON (where the statement guarantees us a single value)

So we have a query that returns a JSON string? So how do we get that string into a variable? we know that there is only one item coming back – however, we can’t access that column directly – so we have to get creative! (or maybe not that creative depending on your T-SQL knowledge)

DECLARE @JSON NVARCHAR(MAX) = N'';
SELECT @JSON = (SELECT 
	*
FROM
	sys.configurations AS C
ORDER BY
	C.[configuration_id]
FOR JSON AUTO);
PRINT @JSON
GO
/*
OR
*/
DECLARE @JSON NVARCHAR(MAX) = N'';
SELECT @JSON = (SELECT 
	*
FROM
	sys.configurations AS C
ORDER BY
	C.[configuration_id]
FOR JSON AUTO);
PRINT @JSON
GO

And there we have it. Now we have a piece of JSON that we have gained directly from a SQL Server table placed straight into a T-SQL variable;

I hope this has helped on your SQL Server JSON journey. We’ll see more real soon.

Have a great day

Cheers

Marty

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JSON data and a T-SQL variable.

JSON, SQL Server and Esacpe Characters of the non-printable kind

G’day,

We observed in a previous installment that JSON uses the backslash character “\” as the escape character.

However, what happens if we actually want a backslash in our sting.

Well, We just escape that with another backslash

SELECT STRING_ESCAPE('\' , 'json');

Which gives (simply)

\\

So when we see a JSON document like this

[
  {
    "Character": "\n"
  },
  {
    "Character": "\r"
  }
]

Then we might wonder

  • Has something gone wrong?
  • Is this valid JSON?

The answer would be that everything is fine and this is perfectly valid JSON.

Why?

Because \r and \n are both non-printable characters.

You’ll see this is valid if you use STRING_ESCAPE

SELECT STRING_ESCAPE(CHAR(10) , 'json') AS [Character]
UNION
SELECT STRING_ESCAPE(CHAR(13) , 'json');

Which gives

Char(10) – ASCII 10 – is the new line character, while CHAT(13) – ASCII 13 – is the carriage return character.

If you’d like to look at other examples of non printable characters then you can play with the STRING_EXCAPE and ASCII T-SQL functions

I hope this has helped on your SQL Server JSON journey. We’ll see more real soon.

Have a great day

Cheers

Marty

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JSON, SQL Server and Esacpe Characters of the non-printable kind

JSON, SQL Server and Escape Characters of the printable kind

We know that certain characters in SQL need escaping – an example is the single quote – ‘

SELECT 'This is a single quote '' mark' AS EscapedCharacter;

Microsoft have even given us a special function for escaping certain characters – and at present (May 2019) – it only does JSON. So lets have a look

SELECT STRING_ESCAPE('"This is a quote ". This is a backslash \"','json')  AS EscapedCharacter;

So, that’s an option that we always have.

But let’s create a table with some special JSON characters in it and see how FOR JSON AUTO treats it

IF OBJECT_ID('temp..#Characters') IS NOT NULL
	BEGIN
		DROP TABLE [#Characters];
	END

CREATE TABLE #Characters
(
	 CharacterID INT IDENTITY(1,1) NOT NULL
	,String NVARCHAR(100)
);

INSERT INTO #Characters (String) VALUES
('https:\\en.wikipedia.org\wiki\Albert_Einstein'),
('"This could be a quote"'),
('''This could be another quote''');

SELECT * FROM #Characters FOR JSON AUTO;

And we get the JSON

[
  {
    "CharacterID": 1,
    "String": "https:\\\\en.wikipedia.org\\wiki\\Albert_Einstein"
  },
  {
    "CharacterID": 2,
    "String": "\"This could be a quote\""
  },
  {
    "CharacterID": 3,
    "String": "'This could be another quote'"
  }
]

Which is perfectly escaped.

Notice that the JSON escape character is a backslash – \

Also notice that although we escaped the single quote character ‘ in the SQL table, the FOR JSON AUTO clause knew this was escaped in the table and addressed it appropriately in the resulting JSON.

We’ll look at more escaping of characters in the next installment.

I hope this has helped on your SQL Server JSON journey. We’ll see more real soon.

Have a great day

Cheers

Marty

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JSON, SQL Server and Esacpe Characters of the printable kind

SQL Server and JSON – JSON PATH

So, we’ve seen how FOR JSON AUTO works. It’s fairly simple – just add the clause onto the end of the SQL statement

But what happens if we need more control over how the JSON will look?

Well, we have another clause that’ll do that for us.

Similar to FOR JSON AUTO – this one is called FOR JSON PATH

For Example using out FOR JSON AUTO clause we ended up with JSON that looked like this. (I’ve just selected the TOP 1 row of the sys.configurations table here)

[
  {
    "configuration_id": 101,
    "Configuration name": "recovery interval (min)",
    "Configuration Value": 0,
    "minimum": 0,
    "maximum": 32767,
    "value_in_use": 0,
    "description": "Maximum recovery interval in minutes",
    "is_dynamic": true,
    "is_advanced": true
  }
]

But what if we wanted our JSON to look something like this

[
  {
    "configuration_id": 101,
    "Configuration_Property": {
      "Configuration name": "recovery interval (min)",
      "Value": 0,
      "minimum": 0,
      "maximum": 32767,
      "value_in_use": 0,
      "description": "Maximum recovery interval in minutes",
      "is_dynamic": true,
      "is_advanced": true
    }
  }
]

Well, we use FOR JSON PATH – and we also alias the T-SQL code. You’ll notice that there is a new block called “Configuration_Property” that contains 8 of the properties.

so, here’s the query that produced the above output

SELECT 
	 [configuration_id]                           = C.configuration_id
	,[Configuration_Property.Configuration name]  = C.[name]
	,[Configuration_Property.Value]               = C.[value]
	,[Configuration_Property.minimum]             = C.minimum
	,[Configuration_Property.maximum]             = C.maximum
	,[Configuration_Property.value_in_use]        = C.value_in_use
	,[Configuration_Property.description]         = C.[description]
	,[Configuration_Property.is_dynamic]          = C.is_dynamic
	,[Configuration_Property.is_advanced]         = C.is_advanced
FROM 
	sys.configurations AS C
ORDER BY
	C.configuration_id
FOR JSON PATH;

I think that although the JSON represents the same information, it’s easier to read. I also think it can make queries against the JSON easier to understand, but we’ll have a look at that in a later instalment.

I hope this helps

Have a great day.

Cheers

Marty.