fix(query): align full outer USING nullability

[sundy-li]

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Summary

• Mark the visible USING/NATURAL join key as nullable for FULL OUTER JOIN so the planned result schema matches the hash-join output schema.
• Replace the debug-only projection schema assertion with an internal error that reports the column name, index, and mismatched types.
• Add a service regression test that checks the planned and executed schema for a FULL OUTER JOIN ... USING query.

Changes

1. Updated resolve_using() in the join binder to preserve nullable result metadata for visible FULL OUTER JOIN keys.
2. Updated build_result_projection() to return ErrorCode::Internal instead of panicking on schema mismatches.
3. Added a regression test covering nullable INT64 output from FULL OUTER JOIN ... USING.

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Pair with the reviewer to explain why

Attempted:

• cargo test -p databend-query --test it sql::schema::test_full_outer_join_using_reports_nullable_result_schema -- --exact

Blocked in this environment by missing toolchain dependencies:

• clang/mold linker configuration from .cargo/config.toml
• protoc required by databend-meta-types and databend-meta-proto build scripts

Type of change

• Bug fix (non-breaking change which fixes an issue)

Fixes #19568

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This change is 

[sundy-li]

For USING, unqualified name resolution keeps only the one binding whose visibility stays visible (see BindContext::match_column_binding), so this branch is still making x resolve to a single input column. For FULL OUTER JOIN, that is not the merged USING semantics: SELECT x FROM (SELECT 1 AS x) a FULL OUTER JOIN (SELECT 2 AS x) b USING (x) should surface 1, 2, but the surviving left-side binding yields 1, NULL on the right-only row. This patch aligns the schema with the current nullable left-column behavior instead of fixing the merged-key behavior. The fix needs to produce a coalesced visible USING expression (or equivalent) and the regression test should assert row values, not only the inferred type.

[github-actions]

🤖 CI Job Analysis

Workflow: 23586788527

📊 Summary

• Total Jobs: 86
• Failed Jobs: 17
• Retryable: 0
• Code Issues: 17

❌ NO RETRY NEEDED

All failures appear to be code/test issues requiring manual fixes.

🔍 Job Details

• ❌ linux / test_unit: Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone_minio (query, hybrid, parquet): Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone_minio (query, http, parquet): Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone_minio (query, http, native): Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone_minio (query, hybrid, native): Not retryable (Code/Test)
• ❌ linux / sqllogic / cluster (crdb, 2c, 2, http): Not retryable (Code/Test)
• ❌ linux / sqllogic / cluster (duckdb, 4c, http): Not retryable (Code/Test)
• ❌ linux / sqllogic / cluster (query, 4c, hybrid): Not retryable (Code/Test)
• ❌ linux / sqllogic / cluster (crdb, 2c, 2, hybrid): Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone (query, 4c, http): Not retryable (Code/Test)
• ❌ linux / sqllogic / cluster (query, 4c, http): Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone (query, 4c, hybrid): Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone (duckdb, 4c, http): Not retryable (Code/Test)
• ❌ linux / sqllogic / cluster (duckdb, 4c, hybrid): Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone (crdb, 2c, hybrid): Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone (crdb, 2c, http): Not retryable (Code/Test)
• ❌ linux / sqllogic / standalone (duckdb, 4c, hybrid): Not retryable (Code/Test)

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🤖 About

Automated analysis using job annotations to distinguish infrastructure issues (auto-retried) from code/test issues (manual fixes needed).

[sundy-li]

FunctionCall { func_name: "coalesce" } is not executable in this planner path. CI is failing with UnknownFunction: function coalesce does not exist, and the sqllogic failures point directly at NATURAL/FULL OUTER JOIN queries after this rewrite. Please build this expression through the normal type-check / function-resolution path (or use the internal scalar form that execution already understands) instead of hard-coding a raw FunctionCall here.