🐛 fix(ai): 修复多方言执行与 DDL 降级

- SQL 执行：移除 AI 工具和代码块预览中硬编码的 LIMIT 50
- 方言适配：按连接类型和自定义驱动别名生成只读 SQL 预览限流语句
- Oracle 兼容：Oracle、自定义 Oracle 和达梦改用 ROWNUM 语法限制行数
- 权限降级：获取表 DDL 失败时自动降级为字段元数据摘要
- 上下文优化：手动添加表结构上下文时复用同一套 DDL 降级逻辑
- 测试覆盖：新增 AI SQL 限流和表结构降级单元测试
Refs #418

frontend/src/components/AIChatPanel.tsx

@@ -25,6 +25,8 @@ import {
     buildMissingProviderNotice,
     buildModelFetchFailedNotice,
 } from '../utils/aiComposerNotice';
+import { buildAIReadonlyPreviewSQL } from '../utils/aiSqlLimit';
+import { resolveAITableSchemaToolResult } from '../utils/aiTableSchemaTool';
 
 interface AIChatPanelProps {
     width?: number;
@@ -1145,12 +1147,15 @@ SELECT * FROM users WHERE status = 1;
                             try {
                                 const safeDbName = args.dbName ? String(args.dbName).trim() : '';
                                 const safeTable = args.tableName ? String(args.tableName).trim() : '';
-                                const { DBShowCreateTable } = await import('../../wailsjs/go/app/App');
-                                const ddlRes = await DBShowCreateTable(buildRpcConnectionConfig(conn.config) as any, safeDbName, safeTable);
-                                if (ddlRes?.success) {
-                                    resStr = typeof ddlRes.data === 'string' ? ddlRes.data : JSON.stringify(ddlRes.data);
-                                    success = true;
-                                } else { resStr = ddlRes?.message || 'Failed to fetch DDL'; }
+                                const { DBShowCreateTable, DBGetColumns } = await import('../../wailsjs/go/app/App');
+                                const rpcConfig = buildRpcConnectionConfig(conn.config) as any;
+                                const toolResult = await resolveAITableSchemaToolResult({
+                                    tableName: safeTable,
+                                    fetchDDL: () => DBShowCreateTable(rpcConfig, safeDbName, safeTable),
+                                    fetchColumns: () => DBGetColumns(rpcConfig, safeDbName, safeTable),
+                                });
+                                resStr = toolResult.content;
+                                success = toolResult.success;
                             } catch (e: any) {
                                 resStr = `获取建表语句失败: ${e?.message || e}`;
                             }
@@ -1173,14 +1178,8 @@ SELECT * FROM users WHERE status = 1;
                                     }
                                 }
                                 const { DBQuery } = await import('../../wailsjs/go/app/App');
-                                // 只对只读查询自动追加 LIMIT，写操作（UPDATE/DELETE/INSERT等）不追加
-                                const sqlTrimmed = safeSql.replace(/;\s*$/, ''); // 去掉末尾分号防止拼接出 "; LIMIT 50"
-                                const sqlFirstWord = sqlTrimmed.trimStart().split(/\s/)[0]?.toLowerCase() || '';
-                                const isReadQuery = ['select', 'show', 'describe', 'desc', 'explain', 'with'].includes(sqlFirstWord);
-                                const finalSql = (isReadQuery && !sqlTrimmed.toLowerCase().includes('limit'))
-                                    ? sqlTrimmed + ' LIMIT 50'
-                                    : sqlTrimmed;
-                                const qRes = await DBQuery(buildRpcConnectionConfig(conn.config) as any, safeDbName, safeSql + (safeSql.toLowerCase().includes('limit') ? '' : ' LIMIT 50'));
+                                const finalSql = buildAIReadonlyPreviewSQL(conn.config?.type || '', safeSql, 50, conn.config?.driver || '');
+                                const qRes = await DBQuery(buildRpcConnectionConfig(conn.config) as any, safeDbName, finalSql);
                                 if (qRes?.success) {
                                     const rows = Array.isArray(qRes.data) ? qRes.data : [];
                                     const limitedRows = rows.slice(0, 50);

frontend/src/components/ai/AIChatInput.tsx

@@ -2,10 +2,11 @@ import React from 'react';
 import { Input, Select, AutoComplete, Tooltip, Modal, Checkbox, Spin, message, Button, Tag } from 'antd';
 import { DatabaseOutlined, SendOutlined, TableOutlined, SearchOutlined, PictureOutlined, ExclamationCircleFilled } from '@ant-design/icons';
 import { useStore } from '../../store';
-import { DBGetTables, DBShowCreateTable, DBGetDatabases } from '../../../wailsjs/go/app/App';
+import { DBGetTables, DBShowCreateTable, DBGetDatabases, DBGetColumns } from '../../../wailsjs/go/app/App';
 import type { OverlayWorkbenchTheme } from '../../utils/overlayWorkbenchTheme';
 import type { AIComposerNotice } from '../../utils/aiComposerNotice';
 import { buildRpcConnectionConfig } from '../../utils/connectionRpcConfig';
+import { resolveAITableSchemaToolResult } from '../../utils/aiTableSchemaTool';
 
 interface AIChatInputProps {
     input: string;
@@ -202,24 +203,21 @@ export const AIChatInput: React.FC<AIChatInputProps> = ({
                 if (activeContextItems.find(c => c.dbName === dbName && c.tableName === tableName)) {
                     continue;
                 }
-                const res = await DBShowCreateTable(buildRpcConnectionConfig(conn.config) as any, dbName, tableName);
-                let createSql = '';
-                if (res.success && res.data) {
-                    if (typeof res.data === 'string') {
-                        createSql = res.data;
-                    } else if (Array.isArray(res.data) && res.data.length > 0) {
-                        const row = res.data[0];
-                        createSql = (Object.values(row).find(v => typeof v === 'string' && (v.toUpperCase().includes('CREATE TABLE') || v.toUpperCase().includes('CREATE'))) || Object.values(row)[1] || Object.values(row)[0]) as string;
-                    }
-                } else {
-                    message.error(`获取表 ${dbName}.${tableName} 结构失败: ` + (res.message || '未知错误'));
+                const rpcConfig = buildRpcConnectionConfig(conn.config) as any;
+                const schemaResult = await resolveAITableSchemaToolResult({
+                    tableName,
+                    fetchDDL: () => DBShowCreateTable(rpcConfig, dbName, tableName),
+                    fetchColumns: () => DBGetColumns(rpcConfig, dbName, tableName),
+                });
+                if (!schemaResult.success) {
+                    message.error(`获取表 ${dbName}.${tableName} 结构失败: ${schemaResult.content}`);
                 }
-                
-                if (createSql) {
+
+                if (schemaResult.success && schemaResult.content) {
                     addAIContext(connectionKey, {
                         dbName: dbName,
                         tableName: tableName,
-                        ddl: createSql
+                        ddl: schemaResult.content
                     });
                     addedCount++;
                 }

frontend/src/components/ai/AIMessageBubble.tsx

@@ -15,6 +15,7 @@ import {
     parseJVMDiagnosticPlan,
     resolveJVMDiagnosticPlanTargetTabId,
 } from '../../utils/jvmDiagnosticPlan';
+import { buildAIReadonlyPreviewSQL } from '../../utils/aiSqlLimit';
 
 // 🔧 性能优化：将 ReactMarkdown 包装为 Memo 组件并提取固定的 plugins
 const remarkPlugins = [remarkGfm];
@@ -260,7 +261,13 @@ const AIBlockHashRender = ({ match, darkMode, overlayTheme, children, activeConn
         setPreviewData(null);
         try {
             const { DBQuery } = await import('../../../wailsjs/go/app/App');
-            const res = await DBQuery(activeConnectionConfig, activeDbName || '', displayText + ' LIMIT 50');
+            const previewSql = buildAIReadonlyPreviewSQL(
+                activeConnectionConfig?.type || '',
+                displayText,
+                50,
+                activeConnectionConfig?.driver || '',
+            );
+            const res = await DBQuery(activeConnectionConfig, activeDbName || '', previewSql);
             if (res.success && Array.isArray(res.data)) {
                 const rows = res.data as any[];
                 const cols = rows.length > 0 ? Object.keys(rows[0]) : [];

frontend/src/utils/aiSqlLimit.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, it } from 'vitest';
+
+import { buildAIReadonlyPreviewSQL } from './aiSqlLimit';
+
+describe('buildAIReadonlyPreviewSQL', () => {
+  it('limits Oracle readonly SQL with ROWNUM instead of MySQL LIMIT', () => {
+    const sql = buildAIReadonlyPreviewSQL('oracle', 'SELECT 1 FROM DUAL;', 50);
+
+    expect(sql).toBe('SELECT * FROM (SELECT 1 FROM DUAL) WHERE ROWNUM <= 50');
+    expect(sql.toLowerCase()).not.toContain('limit');
+  });
+
+  it('does not add another limit when Oracle SQL already limits rows', () => {
+    expect(buildAIReadonlyPreviewSQL('oracle', 'SELECT * FROM users WHERE ROWNUM <= 10', 50))
+      .toBe('SELECT * FROM users WHERE ROWNUM <= 10');
+    expect(buildAIReadonlyPreviewSQL('oracle', 'SELECT * FROM users FETCH FIRST 10 ROWS ONLY', 50))
+      .toBe('SELECT * FROM users FETCH FIRST 10 ROWS ONLY');
+  });
+
+  it('resolves custom Oracle drivers from the driver alias', () => {
+    expect(buildAIReadonlyPreviewSQL('custom', 'SELECT 1 FROM DUAL;', 50, 'oracle'))
+      .toBe('SELECT * FROM (SELECT 1 FROM DUAL) WHERE ROWNUM <= 50');
+  });
+
+  it('keeps MySQL-family SQL on LIMIT syntax', () => {
+    expect(buildAIReadonlyPreviewSQL('mysql', 'SELECT * FROM users', 50))
+      .toBe('SELECT * FROM users LIMIT 50 OFFSET 0');
+  });
+
+  it('keeps PostgreSQL-compatible and ClickHouse SQL on LIMIT syntax', () => {
+    expect(buildAIReadonlyPreviewSQL('postgres', 'SELECT * FROM users', 50))
+      .toBe('SELECT * FROM users LIMIT 50 OFFSET 0');
+    expect(buildAIReadonlyPreviewSQL('kingbase', 'SELECT * FROM users', 50))
+      .toBe('SELECT * FROM users LIMIT 50 OFFSET 0');
+    expect(buildAIReadonlyPreviewSQL('clickhouse', 'SELECT * FROM events', 50))
+      .toBe('SELECT * FROM events LIMIT 50 OFFSET 0');
+  });
+
+  it('limits Dameng readonly SQL with Oracle-compatible ROWNUM syntax', () => {
+    expect(buildAIReadonlyPreviewSQL('dameng', 'SELECT 1 FROM DUAL;', 50))
+      .toBe('SELECT * FROM (SELECT 1 FROM DUAL) WHERE ROWNUM <= 50');
+  });
+
+  it('does not limit non-readonly SQL', () => {
+    expect(buildAIReadonlyPreviewSQL('oracle', 'UPDATE users SET name = \'a\';', 50))
+      .toBe('UPDATE users SET name = \'a\'');
+  });
+});

frontend/src/utils/aiSqlLimit.ts

@@ -0,0 +1,31 @@
+import { buildPaginatedSelectSQL } from './sql';
+import { resolveSqlDialect } from './sqlDialect';
+
+const AI_READONLY_SQL_KEYWORDS = new Set(['select', 'show', 'describe', 'desc', 'explain', 'with', 'pragma', 'values']);
+
+const trimSQLStatement = (sql: string): string => String(sql || '').trim().replace(/;\s*$/, '').trim();
+
+const isAIReadonlySQL = (sql: string): boolean => {
+  const firstWord = trimSQLStatement(sql).trimStart().split(/\s+/)[0]?.toLowerCase() || '';
+  return AI_READONLY_SQL_KEYWORDS.has(firstWord);
+};
+
+const hasExistingRowLimit = (dialect: string, sql: string): boolean => {
+  const text = trimSQLStatement(sql).toLowerCase();
+  if (!text) return false;
+  if (/\blimit\s+\d+\b/.test(text)) return true;
+  if (/\bfetch\s+(first|next)\s+\d+\s+rows?\b/.test(text)) return true;
+  if (/\btop\s*\(?\s*\d+\s*\)?\b/.test(text)) return true;
+
+  return (dialect === 'oracle' || dialect === 'dameng') && /\brownum\b/.test(text);
+};
+
+export const buildAIReadonlyPreviewSQL = (dbType: string, sql: string, limit = 50, driver = ''): string => {
+  const baseSQL = trimSQLStatement(sql);
+  const safeLimit = Math.max(0, Math.floor(Number(limit) || 0));
+  const dialect = resolveSqlDialect(dbType, driver);
+  if (!baseSQL || safeLimit <= 0 || !isAIReadonlySQL(baseSQL) || hasExistingRowLimit(dialect, baseSQL)) {
+    return baseSQL;
+  }
+  return buildPaginatedSelectSQL(dialect, baseSQL, '', safeLimit, 0);
+};

frontend/src/utils/aiTableSchemaTool.test.ts

@@ -0,0 +1,51 @@
+import { describe, expect, it, vi } from 'vitest';
+
+import { resolveAITableSchemaToolResult } from './aiTableSchemaTool';
+
+describe('resolveAITableSchemaToolResult', () => {
+  it('returns DDL directly when DDL fetch succeeds', async () => {
+    const fetchColumns = vi.fn();
+
+    const result = await resolveAITableSchemaToolResult({
+      tableName: 'USERS',
+      fetchDDL: vi.fn().mockResolvedValue({ success: true, data: 'CREATE TABLE USERS (ID NUMBER)' }),
+      fetchColumns,
+    });
+
+    expect(result).toEqual({ success: true, content: 'CREATE TABLE USERS (ID NUMBER)' });
+    expect(fetchColumns).not.toHaveBeenCalled();
+  });
+
+  it('falls back to column metadata when DDL fetch fails due to permissions', async () => {
+    const result = await resolveAITableSchemaToolResult({
+      tableName: 'USERS',
+      fetchDDL: vi.fn().mockResolvedValue({ success: false, message: 'ORA-31603: object not found or insufficient privileges' }),
+      fetchColumns: vi.fn().mockResolvedValue({
+        success: true,
+        data: [
+          { Name: 'ID', Type: 'NUMBER', Nullable: 'NO', Default: null, Comment: '主键' },
+          { Name: 'NAME', Type: 'VARCHAR2(64)', Nullable: 'YES' },
+        ],
+      }),
+    });
+
+    expect(result.success).toBe(true);
+    expect(result.content).toContain('DDL 获取失败，已降级为字段元数据摘要');
+    expect(result.content).toContain('ORA-31603');
+    expect(result.content).toContain('可用字段：ID, NAME');
+    expect(result.content).toContain('"field":"ID"');
+    expect(result.content).toContain('"type":"NUMBER"');
+  });
+
+  it('returns a combined failure when both DDL and column metadata fail', async () => {
+    const result = await resolveAITableSchemaToolResult({
+      tableName: 'USERS',
+      fetchDDL: vi.fn().mockResolvedValue({ success: false, message: 'DDL permission denied' }),
+      fetchColumns: vi.fn().mockResolvedValue({ success: false, message: 'columns permission denied' }),
+    });
+
+    expect(result.success).toBe(false);
+    expect(result.content).toContain('DDL permission denied');
+    expect(result.content).toContain('columns permission denied');
+  });
+});

frontend/src/utils/aiTableSchemaTool.ts

@@ -0,0 +1,69 @@
+type ToolQueryResult = {
+  success?: boolean;
+  data?: unknown;
+  message?: string;
+};
+
+type ResolveAITableSchemaToolResultParams = {
+  tableName: string;
+  fetchDDL: () => Promise<ToolQueryResult>;
+  fetchColumns: () => Promise<ToolQueryResult>;
+};
+
+const stringifyToolData = (data: unknown): string => (
+  typeof data === 'string' ? data : JSON.stringify(data)
+);
+
+const firstStringValue = (row: Record<string, unknown>, keys: string[]): string => {
+  for (const key of keys) {
+    const value = row[key];
+    if (value !== undefined && value !== null) {
+      return String(value);
+    }
+  }
+  return '';
+};
+
+const normalizeAIColumn = (raw: unknown) => {
+  const row = (raw && typeof raw === 'object') ? raw as Record<string, unknown> : {};
+  const keys = Object.keys(row);
+  return {
+    field: firstStringValue(row, ['Field', 'field', 'COLUMN_NAME', 'column_name', 'Name', 'name']) || (keys.length > 0 ? String(row[keys[0]] ?? '') : ''),
+    type: firstStringValue(row, ['Type', 'type', 'DATA_TYPE', 'data_type']) || (keys.length > 1 ? String(row[keys[1]] ?? '') : ''),
+    nullable: firstStringValue(row, ['Null', 'null', 'IS_NULLABLE', 'is_nullable', 'Nullable', 'nullable']),
+    default: firstStringValue(row, ['Default', 'default', 'COLUMN_DEFAULT', 'column_default', 'DefaultValue']),
+    comment: firstStringValue(row, ['Comment', 'comment', 'COLUMN_COMMENT', 'column_comment', 'Description']),
+  };
+};
+
+const buildColumnFallbackContent = (tableName: string, ddlError: string, columns: unknown[]): string => {
+  const normalizedColumns = columns.map(normalizeAIColumn).filter((column) => column.field.trim());
+  const fieldNames = normalizedColumns.map((column) => column.field).join(', ');
+  return [
+    `⚠️ 表 ${tableName} 的 DDL 获取失败，已降级为字段元数据摘要。`,
+    `DDL 错误：${ddlError || '未知错误'}`,
+    '该结果不包含完整索引、约束、触发器等 DDL 信息；请基于字段列表继续分析，不要因为 DDL 权限失败而停止。',
+    `可用字段：${fieldNames || '无'}`,
+    `详细信息：${JSON.stringify(normalizedColumns)}`,
+  ].join('\n');
+};
+
+export const resolveAITableSchemaToolResult = async ({
+  tableName,
+  fetchDDL,
+  fetchColumns,
+}: ResolveAITableSchemaToolResultParams): Promise<{ success: boolean; content: string }> => {
+  const ddlResult = await fetchDDL();
+  if (ddlResult?.success) {
+    return { success: true, content: stringifyToolData(ddlResult.data) };
+  }
+
+  const ddlError = ddlResult?.message || 'Failed to fetch DDL';
+  const columnResult = await fetchColumns();
+  if (columnResult?.success && Array.isArray(columnResult.data)) {
+    return { success: true, content: buildColumnFallbackContent(tableName, ddlError, columnResult.data) };
+  }
+
+  const columnError = columnResult?.message || 'Failed to fetch columns';
+  return { success: false, content: `获取建表语句失败：${ddlError}；降级获取字段列表也失败：${columnError}` };
+};

frontend/src/utils/sql.ts

@@ -192,7 +192,8 @@ export const buildPaginatedSelectSQL = (
   }
 
   switch (normalizedType) {
-    case 'oracle': {
+    case 'oracle':
+    case 'dameng': {
       const orderedSql = `${base}${orderBy}`;
       const upperBound = safeOffset + safeLimit;
       if (safeOffset <= 0) {