JSONExtractInt64 null extract from string into clickhouse - json

Question

I have a source table:
CREATE TABLE test.source
(
text_json String
)
engine = Memory;
I have a destination table:
CREATE TABLE test.destination
(
column Nullable(Int64)
)
engine = Memory;
I insert to the source:
INSERT INTO test.source (text_json) FORMAT JSONAsString {"column": null};
Then I try to parse json int value and insert into destination
INSERT INTO test.destination (column)
SELECT JSONExtractInt(text_json) FROM test.source;
However, it will insert 0. And it will be a non-deterministic behavior as if I have a real zero beforehand, it will be impossible to differentiate between NULL and 0.
How to parse from JSONString null value into Int64 column AS Null?

Answer 1

You can use JSON_VALUE to extract the string value and pass that to INSERT instead (with implicit or explicit casting):
INSERT INTO test.destination (column)
SELECT JSON_VALUE(text_json, '$.column')
FROM test.source
The result will be NULL:
SELECT * FROM test.destination
┌─column─┐
│ ᴺᵁᴸᴸ │
└────────