fix(kingbase): export table DDL from catalog metadata

[openai0229]

Related issue

N/A - this fix follows a direct error report. No matching open issue was found.

Summary

Exporting a Kingbase table's DDL fails with column c.udt_name does not exist when information_schema.columns omits PostgreSQL-style fields. Read column metadata from the system catalogs and use format_type and pg_get_expr to retain complete type definitions and expressions.

Detect optional identity and generated-column attributes from JDBC result metadata. Preserve identity generation mode and sequence options, quote column names, and retain the column-privilege filter. For MySQL-compatible Kingbase builds, use the same reconstruction rules as sys_dump: attach AUTO_INCREMENT after keys, restore the sequence's last_value, next_value and is_called state, and declare attached enums with ENUM ... NAMES ... so their defaults remain valid. Existing comment escaping and ownership/grant output are retained. Add eight regression tests covering these cases and the original catalog compatibility behavior.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• Commands and results: Java 17, run in the isolated PR worktree; 27 tests passed, zero failures/errors/skips, and the plugin plus reactor dependencies packaged successfully.

mvn -B -f chat2db-community-server/pom.xml \
  -pl :chat2db-community-kingbase -am \
  -Dmaven.test.skip=false -DskipTests=false \
  -Dtest=KingBaseTableDDLTest,KingBaseSQLIdentifierProcessorTest \
  -Dsurefire.failIfNoSpecifiedTests=false \
  -Dmaven.test.failure.ignore=false package
git diff --check

• Manual verification: Deployed the official KingbaseES_V009R003C018B0003_aarch64_Docker.tar image locally and confirmed KingbaseES V009R003C018, database_mode=mysql. Used the repository's default kingbase8-8.6.0.jar driver and directly invoked the PR's compiled KingBaseMetaData.tableDDL. Reproduced the original missing-udt_name error. Seven integration scenarios passed export/recreation and data or metadata checks: ordinary columns/defaults/precision, auto-increment, stored generated columns, an unused AUTO_INCREMENT=3000000000 starting value, enum defaults, arrays, and quoted column names/comments/indexes/grants. Test schemas, roles and attached enum types were removed; all three leftover counts were zero.
• Kingbase PG-mode verification: Deployed the official KingbaseES_V009R001C010B0004_aarch64_Docker.tar image and confirmed KingbaseES V009R001C010, database_mode=pg. Direct invocation of the unchanged PR's KingBaseMetaData.tableDDL with the default Kingbase JDBC driver passed eight integration scenarios: ordinary columns/defaults/precision, ALWAYS identity with a 3000000000 start and nondefault sequence options, BY DEFAULT identity with a 5000000000 start, arrays, schema-qualified PostgreSQL enums, domain-typed columns, stored generated columns, and quoted names/comments/indexes/grants. Each scenario recreated the table from the exported DDL and checked metadata and inserts. Explicit values were rejected for ALWAYS identity and accepted for BY DEFAULT identity; domain NOT NULL remained enforced. PostgreSQL enums did not use the MySQL NAMES clause. Cleanup left zero test schemas or roles.
• Additional verification: The final catalog queries passed PostgreSQL 17.10 checks for standalone enum references and identity metadata; the temporary schema was rolled back. Earlier PostgreSQL checks also covered dropped columns and column privileges.
• Server capability limit: This Kingbase build rejects VIRTUAL generated-column syntax when creating a fixture; that scenario is explicitly not counted as an integration pass.
• UI evidence: N/A - database metadata generation only.

Risk and compatibility

• Public API or stored data: N/A - no API or application-storage changes; exported column DDL now uses the database's complete type spelling.
• Database or driver compatibility: Real Kingbase validation used V009R003C018 in MySQL mode and V009R001C010 in PG mode, both with the configured default JDBC driver. The exact reported V009R003C011PS021 patch build remains untested.
• Network, privacy, or security: Metadata reads retain column access checks and bound table/schema filters. Sequence identifiers are quoted and escaped; exporting does not modify the source database. The emitted SQL restores the destination auto-increment state.
• Community / Local / Pro boundary: N/A - no edition-specific behavior changes.
• Backward compatibility: Catalog results without attidentity or attgenerated remain supported. Identity sequence lookup is only performed for identity columns; unavailable sequence metadata raises an error instead of silently changing the definition.

Reviewer map

• Start here: SqlConstant.COLUMN_SQL, IDENTITY_SEQUENCE_SQL and SEQUENCE_STATE_SQL, then KingBaseMetaData.tableDDL, appendIdentityOptions and appendAutoIncrement; regression coverage is in KingBaseTableDDLTest.
• Failure condition: Table DDL export against a compatibility view without udt_name; also verify complete type/default/identity definitions on the target Kingbase version.
• Rollback or disable path: Revert this PR. No migration or stored-data rollback is required.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: Codex implemented the change, added regression tests, reviewed the diff, and ran the reported verification. Real Kingbase V9R3C18 MySQL mode, V9R1C10 PG mode, and PostgreSQL 17 verification is described above; the exact reported patch build remains unverified.