[coverage] Conformance findings: PARAMQUERY-021

失败的 xfail 名为 “DECIMAL target — a scale-less DECIMAL declaration must not truncate the value’s fractional digits”，并在 coverage PR 1179 的 tests/ 下被引用。首先定位 DBSQLParameterType.DECIMAL 的 Thrift 参数绑定路径，并针对 connector 运行覆盖率测试。当已声明、无 scale 以及声明不足的 DECIMAL target 都能保留值的每一位小数且不发生截断时，即视为完成。

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

• PARAMQUERY-021 [thrift]: Thrift path truncates a scale-less DECIMAL target: '123.45' bound as DBSQLParameterType.DECIMAL rides with scale 0, so SELECT :v returns 123, destroying the fractional digits
  • failing test: DECIMAL target — a scale-less DECIMAL declaration must not truncate the value’s fractional digits [xfail: thrift] (see the coverage PR diff under tests/)
• PARAMQUERY-021: Thrift path truncates a scale-less DECIMAL target: '123.45' bound as DBSQLParameterType.DECIMAL is sent with scale 0, so SELECT :v returns 123 instead of 123.45, silently destroying the value's fractional digits (the SEA/kernel path returns 123.45 correctly)

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-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/1179