[coverage] Conformance findings: PARAMQUERY-021

Bắt đầu bằng cách xác định phần xử lý DecimalParameter và đường dẫn liên kết tham số trong databricks-sql-python, sau đó so sánh chúng với test bị lỗi test_decimal_target_type_never_truncates_bound_scale trong coverage PR. Chạy conformance test được tham chiếu cho thrift và sea; được xem là hoàn tất khi DECIMAL(10,2) tường minh được liên kết chính xác và các giá trị giữ lại mọi chữ số phần thập phân đã khai báo hoặc có từ nguồn mà không bị cắt ngắn.

Summary

Surfaced by the multi-language coverage fan-out while conformance-testing these SPEC-IDs against databricks/databricks-sql-python. 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-python) is fixed, then flips green as a tripwire.

Findings

• PARAMQUERY-021 [thrift]: DecimalParameter with explicit precision/scale renders DECIMAL(scale,precision) instead of DECIMAL(precision,scale), so a declared DECIMAL(10,2) target is sent as DECIMAL(2,10) and the server rejects it (INVALID_PARAMETER_MARKER_VALUE.INVALID_DATA_TYPE, SQLSTATE 22023)
  • failing test: test_decimal_target_type_never_truncates_bound_scale (see the coverage PR diff under tests/)
• PARAMQUERY-021 [sea]: DecimalParameter with explicit precision/scale renders DECIMAL(scale,precision) instead of DECIMAL(precision,scale), so a declared DECIMAL(10,2) target becomes DECIMAL(2,10) and the kernel rejects the bind with ProgrammingError "DECIMAL scale must be in 0..=precision"
  • failing test: test_decimal_target_type_never_truncates_bound_scale (see the coverage PR diff under tests/)
• PARAMQUERY-021: DecimalParameter with explicit precision/scale renders the cast expression as DECIMAL(scale,precision) instead of DECIMAL(precision,scale), so a declared DECIMAL(10,2) target is sent as DECIMAL(2,10) and every bind with an explicitly declared decimal target fails (thrift: server INVALID_PARAMETER_MARKER_VALUE.INVALID_DATA_TYPE / SQLSTATE 22023; kernel: ProgrammingError "DECIMAL scale must be in 0..=precision")

Reproduce & Expected

PARAMQUERY-021 — Verify that declaring a DECIMAL/NUMERIC target type for a bound parameter never silently drops fractional digits.

Reproduce:

SELECT ? AS v
SELECT ? AS v
SELECT ? AS v

Expected (per the shared spec):

• All three binds prepare and execute successfully.
• (a) The declared DECIMAL(10,2) accommodates the value, so the parameter rides as that decimal type and the value compares numerically equal to 123.45 with both fractional digits intact.
• (b) THE CORE GUARANTEE: with no declared scale, the value is still 123.45 -- NOT 123. Assert the value, not the reported column type: a conforming driver may legitimately deliver this as a decimal the server inferred from the literal OR as the lossless text/string form, so the type is implementation latitude while the VALUE is the contract.
• (c) The value's own scale (4) is authoritative over the under-declared target scale (2): all four fractional digits survive. A result of 123.45 (or 123) is a truncation violation.

Context

• The behavior was first fixed in a DIFFERENT driver — reference PR: https://github.com/databricks/databricks-odbc/pull/167 — which seeded the shared language-neutral spec. This issue tracks the same conformance gap in databricks/databricks-sql-python; 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/1179