🐛 fix(table-designer): 修复 DuckDB 表设计主键保存失效

- 为 DuckDB 表结构变更补充 ADD PRIMARY KEY 预览 SQL
- 保存前拦截已有主键表的主键替换与删除，避免假成功
- 补充 DuckDB 主键变更判定与 schema SQL 回归测试

frontend/src/components/tableDesignerSchemaSql.ts

@@ -79,6 +79,12 @@ export interface BuildStarRocksMaterializedViewPreviewInput {
   properties?: string;
 }
 
+const collectPrimaryKeyColumnKeys = (columns: EditableColumnSnapshot[]): string[] => (
+  columns
+    .filter((col) => col.key === 'PRI')
+    .map((col) => col._key)
+);
+
 const escapeSqlString = (value: string) => String(value || '').replace(/'/g, "''");
 
 const stripIdentifierQuotes = unquoteSqlIdentifierPart;
@@ -607,6 +613,21 @@ const buildDuckDbAlterPreviewSql = (input: BuildAlterTablePreviewInput): string
     }
   });
 
+  const origPKKeys = collectPrimaryKeyColumnKeys(input.originalColumns);
+  const newPKKeys = collectPrimaryKeyColumnKeys(input.columns);
+  const keysChanged = origPKKeys.length !== newPKKeys.length || !origPKKeys.every((key) => newPKKeys.includes(key));
+  if (keysChanged) {
+    if (origPKKeys.length === 0 && newPKKeys.length > 0) {
+      const pkNames = input.columns
+        .filter((col) => col.key === 'PRI')
+        .map((col) => quoteIdentifierPart(col.name, dbType))
+        .join(', ');
+      statements.push(`ALTER TABLE ${tableRef}\nADD PRIMARY KEY (${pkNames});`);
+    } else {
+      statements.push('-- DuckDB 当前仅支持为无主键表新增 PRIMARY KEY；已有主键的修改或删除需要通过重建表完成。');
+    }
+  }
+
   return statements.join('\n');
 };