尝试使用 C++ 连接器从 mariadb 读取多个结果集，命令“不同步？”

Question

使用 mysql c++ 连接器和以下存储过程（手动工作）

DELIMITER $$
CREATE PROCEDURE sp_getvalues()
BEGIN
    SELECT max(a) FROM A;
    SELECT max(b1), min(b2) FROM B;
    SELECT sum(x) FROM C;
END
$$
DELIMITER ;

DELIMITER $$

以下 C++ 代码给出错误：

Commands out of sync; you can't run this command now

第一次调用stmt->getResultSet()。应该叫什么？

void test_multiple_query(Connection* con) {
  sql::Statement* stmt = con->createStatement();
  stmt->executeQuery("CALL sp_getvalues()");
  sql::ResultSet* res = stmt->getResultSet(); 
  cout << res->getInt(1) << '\n';
  delete res;
  res = stmt->getResultSet();
  cout << res->getInt(1) << '\t' << res->getInt(2) << '\n';
  delete res;
  res = stmt->getResultSet();
  cout << res->getDouble(1)<< '\n';
  delete res;
  delete stmt;
}

Answer 1

来自 CALL，“如果设置了 CLIENT_MULTI_RESULTS API 标志，CALL 可以返回任意数量的结果集，并且被调用的存储过程可以执行准备好的语句”

在 MariaDB 的 Connector C++ 中，这是通过 property:

完成的

connection_properties["CLIENT_MULTI_RESULTS"]= "true";

con.reset(driver->connect(connection_properties));

MySQL文档有示例：

sql::Driver * driver = get_driver_instance();

std::auto_ptr< sql::Connection > con(driver->connect(url, user, pass));
con->setSchema(database);

std::auto_ptr< sql::PreparedStatement >  pstmt;
std::auto_ptr< sql::ResultSet > res;

pstmt.reset(con->prepareStatement("CALL get_data()"));
res.reset(pstmt->executeQuery());

for(;;)
{
  while (res->next()) {
    cout << "Name: " << res->getString("Name")
         << " Population: " << res->getInt("Population")
         << endl;
  }
  if (pstmt->getMoreResults())
  {
    res.reset(pstmt->getResultSet());
    continue;
  }
  break;
}