How do I perform a string function whilst using OPENJSON WITH? - sql-server

Question

In this example, DT_RowId is a concatenated string. I need to extract out its values, and make them available in a WHERE clause (not shown).
Is there a way to perform string functions on a value as part of a FROM OPENJSON WITH?
Is there a proper way to extract concatenated strings from a value without using a clunky SELECT statement?
Side note: This example is REALLY part of an UPDATE statement, so I'd be using the extracted values in the WHERE clause (not shown here). Also, also: Split is a custom string function we have.
BTW: I have full control of that DT_RowId, and i could make it an array, for example, [42, 1, 1]
declare #jsonRequest nvarchar(max) = '{"DT_RowId":"42_1_14","Action":"edit","Schedule":"1","Slot":"1","Period":"9:00 to 9:30 UPDATED","AMOnly":"0","PMOnly":"0","AllDay":"1"}'
select
(select Item from master.dbo.Split(source.DT_RowId, '_', 0) where ItemIndex = 0) as ID
,source.Schedule
,source.Slot
,source.[Period]
,source.AllDay
,source.PMOnly
,source.AMOnly
from openjson(#jsonRequest, '$')
with
(
DT_RowId varchar(255) '$.DT_RowId' /*concatenated string of row being edited */
,Schedule tinyint '$.Schedule'
,Slot tinyint '$.Slot'
,[Period] varchar(20) '$.Period'
,AllDay bit '$.AllDay'
,PMOnly bit '$.PMOnly'
,AMOnly bit '$.AMOnly'
) as source

Answer 1

Using SQL-Server 2016+ offers a nice trick to split a string fast and position-aware:
select
DTRow.AsJson as DTRow_All_Content
,JSON_VALUE(DTRow.AsJson,'$[0]') AS DTRow_FirstValue
,source.Schedule
,source.Slot
,source.[Period]
,source.AllDay
,source.PMOnly
,source.AMOnly
from openjson(#jsonRequest, '$')
with
(
DT_RowId varchar(255) '$.DT_RowId' /*concatenated string of row being edited */
,Schedule tinyint '$.Schedule'
,Slot tinyint '$.Slot'
,[Period] varchar(20) '$.Period'
,AllDay bit '$.AllDay'
,PMOnly bit '$.PMOnly'
,AMOnly bit '$.AMOnly'
) as source
OUTER APPLY(SELECT CONCAT('["',REPLACE([source].DT_RowId,'_','","'),'"]')) DTRow(AsJson);
The magic is the transformation of 42_1_14 to ["42","1","14"] with some simple string methods. With this you can use JSON_VALUE() to fetch an item by its position.
General hint: If you have full control of DT_RowId you should rather create this JSON array right from the start and avoid hacks while reading this...
update
Just to demonstrate how this would run, if the value was a JSON-array, check this out:
declare #jsonRequest nvarchar(max) = '{"DT_RowId":["42","1","14"]}'
select
source.DT_RowId as DTRow_All_Content
,JSON_VALUE(source.DT_RowId,'$[0]') AS DTRow_FirstValue
from openjson(#jsonRequest, '$')
with
(
DT_RowId NVARCHAR(MAX) AS JSON
) as source;
update 2
Just to add a little to your self-answer:
We must think of JSON as a special string. As there is no native JSON data type, the engine does not know, when the string is a string, and when it is JSON.
Using NVARCHAR(MAX) AS JSON in the WITH-clause allows to deal with the return value again with JSON methods. For example, we could use CROSS APPLY OPENJSON(UseTheValueHere) to dive into nested lists and objects.
Actually there's no need to use this at all. If there are no repeating elements, one could just parse all the values directly:
SELECT JSON_VALUE(#jsonRequest,'$.DT_RowId[0]') AS DTRowId_1
,JSON_VALUE(#jsonRequest,'$.Action') AS [Action]
--and so on...
But this would mean to parse the JSON over and over, which is very expensive.
Using OPENJSON means to read the whole JSON in one single pass (on the current level) and return the elements found (with or without a JSON path) in a derived set (one row for each element).
The WITH-clause is meant to perform kind of PIVOT-action and returns the elements as a multi-column-set. The additional advantage is, that you can specify the data type and - if necessary - a differing JSON path and the column's alias.
You can use any valid JSON path (as well in the WITH-clause as in JSON_VALUE() or in many other places). That means that there are several ways to get the same result. Understanding how the engine works, will enable you to find the most performant approach.

Answer 2

OP here. Just expanding on the answer I accepted by Shnugo, with some details and notes... Hopefully all this might help somebody out there.
I am going to make DT_RowId an array
I will use AS JSON for DT_RowId in the OPENJSON WITH statement
I can then treat it as a json structure, and use JSON_VALUE to extract a value at a specific index
declare #jsonRequest nvarchar(max) = '{"DT_RowId":["42", "1", "14"],"Action":"edit","Schedule":"1","Slot":"1","Period":"9:00 to 9:30 UPDATED","AMOnly":"0","PMOnly":"0","AllDay":"1"}'
select
source.DT_RowId as DTRowId_FULL_JSON_Struct /*the full array*/
,JSON_VALUE(source.DT_RowId,'$[0]') AS JSON_VAL_0 /*extract value at index 0 from json structure*/
,JSON_VALUE(source.DT_RowId,'$[1]') AS JSON_VAL_1 /*extract value at index 1 from json structure*/
,JSON_VALUE(source.DT_RowId,'$[2]') AS JSON_VAL_2 /*extract value at index 2 from json structure*/
,source.DT_RowId_Index0 /*already extracted*/
,source.DT_RowId_Index1 /*already extracted*/
,source.DT_RowId_Index2 /*already extracted*/
,source.Schedule
,source.Slot
,source.Period
,source.AllDay
,source.PMOnly
,source.AMOnly
from openjson(#jsonRequest, '$')
with
(
DT_RowId nvarchar(max) as json /*format as json; do the rest in the SELECT statement*/
,DT_RowId_Index0 varchar(2) '$.DT_RowId[0]' /*When OPENJSON parses a JSON array, the function returns the indexes of the elements in the JSON text as keys.*/
,DT_RowId_Index1 varchar(2) '$.DT_RowId[1]' /*When OPENJSON parses a JSON array, the function returns the indexes of the elements in the JSON text as keys.*/
,DT_RowId_Index2 varchar(2) '$.DT_RowId[2]' /*When OPENJSON parses a JSON array, the function returns the indexes of the elements in the JSON text as keys.*/
,Schedule tinyint '$.Schedule'
,Slot tinyint '$.Slot'
,[Period] varchar(20) '$.Period'
,AllDay bit '$.AllDay'
,PMOnly bit '$.PMOnly'
,AMOnly bit '$.AMOnly'
) as source