SQL Server 2019

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create table test (JsonColumnString  nvarchar(max))
insert into test values (N'[{"CountryId":"A26BF8CF-11A4-4A30-B47E-1CC0C3AC6D69","CountryName":"Circuit_0","Data":[{"SystemType":"Central","SystemTypeId":"EF1FE7E8-6FF9-447E-9DAD-69D0EAAE0642","ReferenceGuid":"04618DE5-B92B-41A3-B0EB-1EE8E4C329CC","System":[{"System":"Bank","SystemId":"3FC19ED5-A08C-4E2B-999C-37D6D83F7D65"}]}],"IsCascade":false},{"CountryId":"4645CEE6-5061-4DB8-8E81-C7B1DB417E38","CountryName":"Circuit_1","Data":[{"SystemType":"State","SystemTypeId":"94E1BEB7-BC8F-4D94-8027-3D53E6C9EB01","ReferenceGuid":"289F5B6D-7CA1-422C-83D3-2688A88D18C5","System":[{"System":"PF","SystemId":"ADA9EBFA-DDCE-4CFA-9A07-10BCFD1232A3","WinterTemp":"75"}],"Cooling":"false"}],"Total":"400"}]');
1 rows affected

SELECT c.SystemId 
FROM OPENJSON((SELECT TOP 1 JsonColumnString FROM test))
WITH (Data NVARCHAR(MAX)  AS JSON) a
CROSS APPLY OPENJSON(a.Data)
WITH (System NVARCHAR(MAX)  AS JSON) b
CROSS APPLY OPENJSON(b.System) 
WITH (SystemId NVARCHAR(MAX) '$.SystemId') c


SystemId


3FC19ED5-A08C-4E2B-999C-37D6D83F7D65

ADA9EBFA-DDCE-4CFA-9A07-10BCFD1232A3


SELECT c.SystemId 
FROM (SELECT TOP 1 JsonColumnString FROM test) t
CROSS APPLY OPENJSON(t.JsonColumnString)
WITH (Data NVARCHAR(MAX)  AS JSON) a
CROSS APPLY OPENJSON(a.Data)
WITH (System NVARCHAR(MAX)  AS JSON) b
CROSS APPLY OPENJSON(b.System) 
WITH (SystemId NVARCHAR(MAX) '$.SystemId') c


SystemId


3FC19ED5-A08C-4E2B-999C-37D6D83F7D65

ADA9EBFA-DDCE-4CFA-9A07-10BCFD1232A3