fix(duckdb): Use ->> operator for Snowflake JSON extraction

[kyle-cheung]

When transpiling a JSON extraction from Snowflake to DuckDB, SQLGlot uses the -> operator. In DuckDB, -> returns a JSON object. When comparing this result to a standard VARCHAR, DATE, or INT, DuckDB throws a Conversion Error: Malformed JSON.

D CREATE OR REPLACE TABLE test AS SELECT JSON('{"test_date": "2025-10-01"}') AS test_date;
D SELECT
    (
      test_date -> '$.test_date'
    ) = '2025-12-01'
  FROM test
  ;
Conversion Error:
Malformed JSON at byte 4 of input: unexpected content after document.  Input: "2025-12-01"

LINE 4:   ) = '2025-12-01'

However this works as expected in Snowflake:

CREATE OR REPLACE TEMPORARY TABLE test_data AS 
SELECT PARSE_JSON('{"test_date": "2025-12-01"') AS test;

SELECT test:test_date = '2025-12-01'
FROM test_data;

To resolve this we need to transpile to the ->> operator, which will work as it does in Snowflake

D SELECT
    (
      test_date ->> '$.test_date'
    ) = '2025-12-01'
  FROM test
  ;
┌────────────────────────────────────────────────┐
│ ((test_date ->> '$.test_date') = '2025-12-01') │
│                    boolean                     │
├────────────────────────────────────────────────┤
│ false                                          │
└────────────────────────────────────────────────┘

In DuckDB ->> still allows chaining

CREATE OR REPLACE TABLE test_json (data JSON);
INSERT INTO test_json VALUES ('{"outer": {"inner": "target_value"}}');
SELECT * FROM test_json;

D SELECT data->>'outer'->>'inner' FROM test_json;
┌────────────────────────────────────┐
│ (("data" ->> 'outer') ->> 'inner') │
│              varchar               │
├────────────────────────────────────┤
│ target_value                       │
└────────────────────────────────────┘
D SELECT data->'outer'->>'inner' FROM test_json;
┌───────────────────────────────────┐
│ (("data" -> 'outer') ->> 'inner') │
│              varchar              │
├───────────────────────────────────┤
│ target_value                      │
└───────────────────────────────────┘

Resolves #6661

[VaggelisD]

Hey @kyle-cheung appreciate the PR but I'm hesitant for this change.

Both Snowflake & Databricks VARIANT accesses produce VARIANT values whereas DuckDB would now produce a VARCHAR:

snowflake> WITH tbl AS (SELECT PARSE_JSON('{"a": 1}') AS col) SELECT SYSTEM$TYPEOF(col:a) FROM tbl;
VARIANT[LOB]

databricks> WITH t AS (SELECT PARSE_JSON('{"a": 1}') AS col) SELECT typeof(col:a) FROM t;
VARIANT

duckdb> WITH tbl AS (SELECT '{"a": 1}'::JSON AS col) select typeof(col ->> '$.a') from tbl;
┌─────────────────────────┐
│ typeof((col ->> '$.a')) │
│         varchar         │
├─────────────────────────┤
│ VARCHAR                 │
└─────────────────────────┘

I'm hesitant for 2 reasons:

1. Chaining may be allowed but it can alter the data types of nested objects, e.g this should probably be preserved as JSON instead of being turned into a VARCHAR

duckdb> WITH tbl AS (SELECT '{"a": {"b": 1}}'::JSON AS col) select col ->> '$.a' from tbl;
┌─────────────────┐
│ (col ->> '$.a') │
│     varchar     │
├─────────────────┤
│ {"b":1}         │
└─────────────────┘

2. Binary operations in Snowflake and DuckDB (for ->>) may work due to coercions but this is not the case for Databricks:

databricks> WITH t AS (SELECT PARSE_JSON('{"a": 1}') AS col) SELECT col:a = 1 FROM t;

[DATATYPE_MISMATCH.BINARY_OP_DIFF_TYPES] Cannot resolve "(variant_get(col, $.a, 'VARIANT') = 1)" due to data type mismatch: the left and right operands of the binary operator have incompatible types ("VARIANT" and "INT"). SQLSTATE: 42K09; line 1, pos 56

cc: @georgesittas curious for your thoughts

[kyle-cheung]

Thanks @georgesittas , I think I may have a workaround that I can follow up with in a separate PR. I'll close this and #6670

Wrapping all JSON extracts in paranthesis will resolve as expected.

CREATE OR REPLACE TABLE test AS SELECT JSON('{"test_bool" : false}') AS test_bool;

-- works
D SELECT test_bool FROM test WHERE test_bool -> '$.test_bool';
┌───────────┐
│ test_bool │
│   json    │
├───────────┤
│  0 rows   │
└───────────┘

-- will not work
D SELECT test_bool FROM test WHERE test_bool -> '$.test_bool' AND 1=1;
Binder Error:
No function matches the given name and argument types 'json_extract(JSON, BOOLEAN)'. You might need to add explicit type casts.
        Candidate functions:
        json_extract(VARCHAR, BIGINT) -> JSON
        json_extract(VARCHAR, VARCHAR) -> JSON
        json_extract(VARCHAR, VARCHAR[]) -> JSON[]
        json_extract(JSON, BIGINT) -> JSON
        json_extract(JSON, VARCHAR) -> JSON
        json_extract(JSON, VARCHAR[]) -> JSON[]


-- will not work
D SELECT test_bool FROM test WHERE NOT test_bool -> '$.test_bool';
Conversion Error:
Failed to cast value to numerical: {"test_bool":false}

LINE 1: SELECT test_bool FROM test WHERE NOT test_bool -> '$.test_bool';
                                             ^

-- works 
D SELECT test_bool FROM test WHERE NOT (test_bool -> '$.test_bool');
┌─────────────────────┐
│      test_bool      │
│        json         │
├─────────────────────┤
│ {"test_bool":false} │
└─────────────────────┘

-- works 
D SELECT test_bool FROM test WHERE NOT (test_bool -> '$.test_bool') AND 1=1;
┌─────────────────────┐
│      test_bool      │
│        json         │
├─────────────────────┤
│ {"test_bool":false} │
└─────────────────────┘

-- Try with another data type 
CREATE OR REPLACE TABLE test AS SELECT JSON('{"test_bool" : 1}') AS test_bool;

D SELECT test_bool FROM test WHERE test_bool -> '$.test_bool' = 1;
Binder Error:
No function matches the given name and argument types 'json_extract(JSON, BOOLEAN)'. You might need to add explicit type casts.
        Candidate functions:
        json_extract(VARCHAR, BIGINT) -> JSON
        json_extract(VARCHAR, VARCHAR) -> JSON
        json_extract(VARCHAR, VARCHAR[]) -> JSON[]
        json_extract(JSON, BIGINT) -> JSON
        json_extract(JSON, VARCHAR) -> JSON
        json_extract(JSON, VARCHAR[]) -> JSON[]

D SELECT test_bool -> '$.test_bool' FROM test WHERE (test_bool -> '$.test_bool') = 1;
┌──────────────────────────────┐
│ (test_bool -> '$.test_bool') │
│             json             │
├──────────────────────────────┤
│ 1                            │
└──────────────────────────────┘