fix: 查询页两个细节修复

1. 点击侧边栏表名插入 db.table 格式(如 log_analytics.access_logs)
   - SchemaSidebar 表名: onInsert(t.name) → onInsert(`${dbName}.${t.name}`)
   - SchemaSidebar 字段名: onInsert(col.Field) → onInsert(`${t.name}.${col.Field}`)
2. 查询不存在的表应显示错误而非'无结果数据'
   - QueriesPage handleExecute: 检查 res.error 字段,有错误则 setError + 不设 result

frontend/src/components/SchemaSidebar.tsx

@@ -498,8 +498,8 @@ export default function SchemaSidebar({ instanceId, database, dbType, onInsert }
                                       <Table2 className="w-2.5 h-2.5 text-blue-400 flex-shrink-0" />
                                       <span
                                         className="font-mono truncate flex-1 text-left hover:text-blue-400 transition-colors"
-                                        onClick={(e) => { e.stopPropagation(); onInsert(t.name); }}
-                                        title="点击插入表名"
+                                        onClick={(e) => { e.stopPropagation(); onInsert(`${dbName}.${t.name}`); }}
+                                        title="点击插入 库名.表名"
                                       >
                                         {t.name}
                                       </span>
@@ -519,7 +519,7 @@ export default function SchemaSidebar({ instanceId, database, dbType, onInsert }
                                           tableColumns.map(col => (
                                             <button
                                               key={col.Field}
-                                              onClick={() => onInsert(col.Field)}
+                                              onClick={() => onInsert(`${t.name}.${col.Field}`)}
                                               className="flex items-center gap-1.5 w-full px-2 py-0.5 text-[10px] hover:bg-[var(--dg-bg-hover)] transition-colors"
                                               title={`${col.Type} ${col.Null === 'NO' ? 'NOT NULL' : ''}`}
                                             >

frontend/src/pages/QueriesPage.tsx

@@ -210,7 +210,12 @@ export default function QueriesPage() {
     setExecuting(true); setError(''); setResult(null);
     try {
       const res = await queryApi.execute({ instance_id: Number(instanceId), database: database || undefined, sql }) as unknown as QueryResult;
-      setResult(res);
+      if (res.error) {
+        setError(res.error);
+        setResult(null);
+      } else {
+        setResult(res);
+      }
       setHistory(prev => [{ id: Date.now(), sql, instance_id: Number(instanceId), database, db_type: dbType, status: 'success', execution_time_ms: res.execution_time_ms || 0, result_preview: JSON.stringify(res.rows?.[0] || {}).substring(0, 100), created_at: new Date().toISOString(), favorite: false }, ...prev]);
     } catch (e: unknown) {
       const raw = (e as { response?: { data?: { detail?: string | Array<{ msg: string }> } } })?.response?.data?.detail;