[coverage] Conformance findings: DATATYPE-042

Start with the DATATYPE-042 expected-failure test in the coverage PR under tests/, then compare the intended behavior with reference PR #644. Trace how databricks-sql-nodejs reports metadata for the two SELECT NULL queries. Done means both live and empty results report STRING for both columns, preserve names and null values, and satisfy the listed row-count assertions.

Summary

Surfaced by the multi-language coverage fan-out while conformance-testing these SPEC-IDs against databricks/databricks-sql-nodejs. Each finding is committed as an expected-failure (xfail) test in the coverage PR — the test asserts the CORRECT (post-fix) behavior and stays red until THIS driver (databricks/databricks-sql-nodejs) is fixed, then flips green as a tripwire.

Findings

• DATATYPE-042 [sea]: SEA/kernel reports NULL_TYPE (TTypeId 16) for an untyped SELECT NULL (VOID) result column instead of its STRING type, so it disagrees with a CAST(NULL AS STRING) sibling in the same result set; Thrift correctly reports STRING_TYPE
  • failing test: untyped NULL column is reported as STRING, matching its CAST(NULL AS STRING) sibling [sea] (see the coverage PR diff under tests/)
• DATATYPE-042: SEA/kernel reports NULL_TYPE (TTypeId 16) for an untyped SELECT NULL (VOID) result column instead of its STRING type, so the column disagrees with a CAST(NULL AS STRING) sibling in the same result set; Thrift correctly reports STRING_TYPE

Reproduce & Expected

DATATYPE-042 — Verify that an UNTYPED NULL column -- a bare SELECT NULL expression, whose Databricks SQL type is VOID (spelled NULL on some surfaces) -- is reported by the driver as its STRING type, identically t…

Reproduce:

SELECT NULL AS untyped_null, CAST(NULL AS STRING) AS typed_null_string
SELECT NULL AS untyped_null, CAST(NULL AS STRING) AS typed_null_string FROM range(1) WHERE 1 = 0

Expected (per the shared spec):

• completes without an exception
• result has 2 column(s)
• col 0 is named untyped_null
• col 1 is named typed_null_string
• result has exactly 1 row(s)
• col untyped_null, row 0 is null
• col typed_null_string, row 0 is null
• completes without an exception
• result has 2 column(s)
• col 0 is named untyped_null
• col 1 is named typed_null_string
• result has exactly 0 row(s)
• full assertion contract:

result:
- label: live_data
  no_exception: true
- label: live_data
  column_count: 2
- label: live_data
  column:
    index: 0
    name: untyped_null
- label: live_data
  column:
    index: 1
    name: typed_null_string
- label: live_data
  column_reported_type:
    name: untyped_null
    equals: STRING
- label: live_data
  column_reported_type:
    name: typed_null_string
    equals: STRING
- label: live_data
  column_reported_types_match:
    columns:
    - untyped_null
    - typed_null_string
- label: live_data
  row_count: 1
- label: live_data
  column:
    name: untyped_null
    is_null: true
- label: live_data
  column:
    name: typed_null_string
    is_null: true
- label: live_data
  column_data_agrees_with_reported_type:
    columns:
    - untyped_null
    - typed_null_string
- label: empty_result
  no_exception: true
- label: empty_result
  column_count: 2
- label: empty_result
  column:
    index: 0
    name: untyped_null
- label: empty_result
  column:
    index: 1
    name: typed_null_string
- label: empty_result
  column_reported_type:
    name: untyped_null
    equals: STRING
- label: empty_result
  column_reported_type:
    name: typed_null_string
    equals: STRING
- label: empty_result
  column_reported_types_match:
    columns:
    - untyped_null
    - typed_null_string
- label: empty_result
  row_count: 0

Context

• The behavior was first fixed in a DIFFERENT driver — reference PR: https://github.com/adbc-drivers/databricks/pull/644 — which seeded the shared language-neutral spec. This issue tracks the same conformance gap in databricks/databricks-sql-nodejs; the reference PR is for cross-referencing the intended behavior, NOT a change to this repo.
• Coverage PR carrying the reproducing xfail test(s): https://github.com/databricks/databricks-driver-test/pull/1258