🐛 fix(query-editor): 修复多数据源大查询限流失效

- SQL限流：抽取查询自动限流工具，修复 SELECT 判断大小写不一致导致限制未生效
- 方言适配：按 Oracle/Dameng、SQL Server、MySQL/PostgreSQL 等方言分别注入行数限制
- 自定义驱动：支持 custom 连接根据 driver 解析 Oracle、PostgreSQL、SQL Server 等方言
- MongoDB修复：修正 db.collection.find() 解析边界，并对 find/只读 aggregate 下推 limit
- Oracle优化：DSN 增加 PREFETCH_ROWS 和 LOB FETCH 参数，减少大结果集拉取开销
- 测试覆盖：补充 SQL 方言矩阵、MongoDB 限流和 Oracle DSN 参数测试
Refs #424

frontend/src/utils/queryAutoLimit.test.ts

@@ -0,0 +1,110 @@
+import { describe, expect, it } from 'vitest';
+
+import { applyQueryAutoLimit } from './queryAutoLimit';
+
+describe('applyQueryAutoLimit', () => {
+  const limitDialects = [
+    'mysql',
+    'mariadb',
+    'diros',
+    'doris',
+    'sphinx',
+    'postgres',
+    'postgresql',
+    'kingbase',
+    'kingbase8',
+    'highgo',
+    'vastbase',
+    'sqlite',
+    'sqlite3',
+    'duckdb',
+    'clickhouse',
+    'tdengine',
+  ];
+
+  it.each(limitDialects)('adds generic LIMIT for %s connections', (dbType) => {
+    expect(applyQueryAutoLimit('SELECT * FROM users', dbType, 500).sql)
+      .toBe('SELECT * FROM users LIMIT 500');
+  });
+
+  it.each([
+    ['oracle'],
+    ['dameng'],
+    ['dm'],
+    ['dm8'],
+  ])('adds FETCH FIRST limit for %s connections', (dbType) => {
+    expect(applyQueryAutoLimit('SELECT * FROM MYCIMLED.EDC_LOG', dbType, 500).sql)
+      .toBe('SELECT * FROM MYCIMLED.EDC_LOG FETCH FIRST 500 ROWS ONLY');
+  });
+
+  it.each([
+    ['sqlserver'],
+    ['mssql'],
+    ['sql_server'],
+    ['sql-server'],
+  ])('adds TOP limit for %s connections', (dbType) => {
+    expect(applyQueryAutoLimit('SELECT * FROM users', dbType, 500).sql)
+      .toBe('SELECT TOP 500 * FROM users');
+  });
+
+  it('adds SQL Server TOP after DISTINCT', () => {
+    expect(applyQueryAutoLimit('SELECT DISTINCT name FROM users', 'sqlserver', 500).sql)
+      .toBe('SELECT DISTINCT TOP 500 name FROM users');
+  });
+
+  it.each([
+    ['oracle', 'SELECT * FROM users FETCH FIRST 500 ROWS ONLY'],
+    ['dm8', 'SELECT * FROM users FETCH FIRST 500 ROWS ONLY'],
+    ['mssql', 'SELECT TOP 500 * FROM users'],
+    ['postgresql', 'SELECT * FROM users LIMIT 500'],
+    ['doris', 'SELECT * FROM users LIMIT 500'],
+    ['sqlite3', 'SELECT * FROM users LIMIT 500'],
+  ])('uses custom driver dialect %s', (driver, expected) => {
+    expect(applyQueryAutoLimit('SELECT * FROM users', 'custom', 500, driver).sql)
+      .toBe(expected);
+  });
+
+  it('keeps trailing semicolon and comments after injected Oracle limit', () => {
+    expect(applyQueryAutoLimit('SELECT * FROM MYCIMLED.EDC_LOG; -- preview', 'oracle', 500).sql)
+      .toBe('SELECT * FROM MYCIMLED.EDC_LOG FETCH FIRST 500 ROWS ONLY; -- preview');
+  });
+
+  it('does not add another generic limit when SQL already limits rows', () => {
+    expect(applyQueryAutoLimit('SELECT * FROM users LIMIT 10', 'mysql', 500).applied)
+      .toBe(false);
+    expect(applyQueryAutoLimit('SELECT * FROM users OFFSET 10 LIMIT 10', 'postgres', 500).applied)
+      .toBe(false);
+  });
+
+  it('does not treat nested LIMIT as the outer query limit', () => {
+    expect(applyQueryAutoLimit('SELECT * FROM (SELECT * FROM users LIMIT 10) t', 'postgres', 500).sql)
+      .toBe('SELECT * FROM (SELECT * FROM users LIMIT 10) t LIMIT 500');
+  });
+
+  it('does not add another Oracle limit when Oracle SQL already limits rows', () => {
+    expect(applyQueryAutoLimit('SELECT * FROM users WHERE ROWNUM <= 10', 'oracle', 500).applied)
+      .toBe(false);
+    expect(applyQueryAutoLimit('SELECT * FROM users FETCH FIRST 10 ROWS ONLY', 'oracle', 500).applied)
+      .toBe(false);
+  });
+
+  it('does not add another SQL Server limit when SQL already uses TOP', () => {
+    expect(applyQueryAutoLimit('SELECT TOP 10 * FROM users', 'sqlserver', 500).applied)
+      .toBe(false);
+  });
+
+  it('adds generic LIMIT before locking clauses', () => {
+    expect(applyQueryAutoLimit('SELECT * FROM users FOR UPDATE', 'mysql', 500).sql)
+      .toBe('SELECT * FROM users LIMIT 500 FOR UPDATE');
+  });
+
+  it('adds generic LIMIT before OFFSET clauses', () => {
+    expect(applyQueryAutoLimit('SELECT * FROM users OFFSET 10', 'postgres', 500).sql)
+      .toBe('SELECT * FROM users LIMIT 500 OFFSET 10');
+  });
+
+  it('does not limit non-select statements', () => {
+    expect(applyQueryAutoLimit('UPDATE users SET name = \'a\'', 'mysql', 500).applied)
+      .toBe(false);
+  });
+});