How to perform dynamic update through MERGE statement in Snowflake? - snowflake-cloud-data-platform

Question

I am performing update from JSON data using MERGE statement. The data contains primary key and the column that was updated from the source system. Since the data contains just the updated column along with primary key, update performed through MERGE is automatically updating other column too to null value. Is there any way through which we could build the update statement dynamically for every row and execute it through MERGE?
create or replace table source_data as
select parse_json(COLUMN1)::variant datacol
from values
('{
"metadata":{"OperationName":"UPDATE"},
"data":{"id":"1234","status":"Active"}
}'),
('{
"metadata":{"OperationName":"UPDATE"},
"data":{"id":"1235","name":"Johny"}
}');
create or replace table employee_destination as
select column1::text as id,
column2::text as name,
column3::text as status
from values
('1234','John','Inactive'),
('1235','Jack','Active');
MERGE into employee_destination as Target using (select datacol:data:id as id,datacol:data:status as status,datacol:data:name name,datacol:metadata:OperationName as operation_name from SOURCE_DATA)
AS Source
ON Target.id = Source.id
when matched AND Source.operation_name = 'UPDATE'
THEN
update set Target.id = Source.id, Target.name = Source.name, Target.status = Source.status;
Current output:
1234 null Active
1235 Johny null
Expected output:
1234 John Active
1235 Johny Inactive
thanks.

Answer 1

Try Below
AS Source
ON Target.id = Source.id
when matched AND Source.operation_name = 'UPDATE'
THEN
update set
--Target.id = Source.id, Why update your PK_ID
Target.name = COALESCE(Source.name,Target.name),
Target.status = COALESCE(Source.status,Target.status);