fix: return MatrixOne foreign key metadata

[iamlinjunhong]

Problem

SQLForeignKeys returns an empty result against MatrixOne even when the requested table has a valid foreign-key constraint. This breaks pyodbc Cursor.foreignKeys() and other ODBC schema-introspection clients.

Tested with:

• MatrixOne main commit c6b2ac9c1eaff0db867e845723a8ce1d2102928f
• matrixone-odbc base bcc10fec25e5cbc7f1febb70f280c0d94bcac2c3
• Windows 11 x64, pyodbc 5.3.0

Root cause

The inherited MySQL catalog query self-joins INFORMATION_SCHEMA.KEY_COLUMN_USAGE foreign-key row A to a second row D representing the referenced primary-key column, then requires D.CONSTRAINT_NAME IS NOT NULL.

MatrixOne exposes the foreign-key row, including all REFERENCED_* fields, but does not expose a separate primary-key row in KEY_COLUMN_USAGE. The self-join therefore removes every valid foreign key. SHOW CREATE TABLE and INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS both confirm that the constraint exists.

Fix

• Detect a MatrixOne server through its server version string.
• On MatrixOne, use the complete foreign-key row directly and require non-null referenced table/column fields.
• Avoid depending on REFERENTIAL_CONSTRAINTS on MatrixOne releases that do not expose it consistently; report the currently supported NO ACTION rule.
• Preserve the historical MySQL self-join, which protects against MySQL bug #51422.
• Log the generated metadata query when query logging is enabled.

Reproduction

CREATE DATABASE fk_repro;
CREATE TABLE fk_repro.parent(id INT PRIMARY KEY);
CREATE TABLE fk_repro.child(
  id INT PRIMARY KEY,
  parent_id INT,
  CONSTRAINT fk_parent FOREIGN KEY(parent_id) REFERENCES fk_repro.parent(id)
);

rows = list(cursor.foreignKeys(
    foreignTable="child", foreignCatalog="fk_repro"
))
assert len(rows) == 1

Before this change, rows is empty. The same result occurs when calling the ANSI/Unicode ODBC API directly.

Before / after

• Before (v9.7.0-mo.3): five valid SQLForeignKeys argument combinations each returned 0 rows.
• After (this branch): direct loading of the newly built myodbc9w.dll returned exactly one row with parent.id -> child.parent_id, KEY_SEQ=1, and FK_NAME=fk_direct.

Regression coverage

mo_odbc_deep now:

• creates a parent/child foreign key fixture;
• verifies that SQLGetFunctions reports SQL_API_SQLFOREIGNKEYS;
• calls SQLForeignKeys and asserts table names, column names, key sequence, foreign-key name, and exact row count.
• distinguishes an older MatrixOne server that exposes no foreign-key row in KEY_COLUMN_USAGE (server known issue) from a driver returning no row when the source metadata exists.

Test scope

• Full Visual Studio 2022 x64 RelWithDebInfo build: PASS; Unicode and ANSI driver targets compile.
• MatrixOne end-to-end catalog SQL against latest main: PASS.
• Direct DLL API verification (bypassing Driver Manager registration):
  • SQLForeignKeysW: PASS
  • query timeout SQLSTATE HYT00: PASS, 1.002 s
  • statement cancellation SQLSTATE HY008: PASS, 0.531 s
• Existing pyodbc/pandas deep suite outside this focused fix: connection, types, Unicode, LOBs, parameters, transactions, bulk fetch, concurrency, network interruption, and server restart were exercised separately.

No Power BI scenario or Power BI-owned environment was modified by this change.