// 从数据库读取一个数据并显示
rc = mysql_query(db_connection, "SELECT order_id FROM test_data WHERE status IS FALSE LIMIT 1");
if (rc != 0) {
    lr_error_message("%s", mysql_error(db_connection));
    mysql_close(db_connection);
    lr_abort();
}
query_result = mysql_use_result(db_connection);
if (query_result == NULL) {
    lr_error_message("%s", mysql_error(db_connection));
    mysql_free_result(query_result);
    mysql_close(db_connection);
    lr_abort();
}
// 如果结果集包含多行数据,需要多次调用 mysql_fetch_row 直到返回NULL
result_row = (char **)mysql_fetch_row(query_result);
if (result_row == NULL) {
    lr_error_message("Did not expect the result set to be empty");
    mysql_free_result(query_result);
    mysql_close(db_connection);
    lr_abort();
}
// 保存参数,用于删除这行数据
lr_save_string(result_row[0], "paramOrderID");
lr_output_message("Order ID is: %s", lr_eval_string("{paramOrderID}"));
mysql_free_result(query_result);

// 在事务里更新一行数据,需要用InnoDB引擎
rc = mysql_query(db_connection, "BEGIN"); //启动事务
if (rc != 0) {
    lr_error_message("%s", mysql_error(db_connection));
    mysql_close(db_connection);
    lr_abort();
}
// 使用 "FOR UPDATE" 锁住要更新的数据行
rc = mysql_query(db_connection, "SELECT order_id FROM test_data WHERE status IS FALSE LIMIT 1 FOR UPDATE");
if (rc != 0) {
    lr_error_message("%s", mysql_error(db_connection));
    mysql_close(db_connection);
    lr_abort();
}
query_result = mysql_use_result(db_connection);
if (query_result == NULL) {
    lr_error_message("%s", mysql_error(db_connection));
    mysql_free_result(query_result);
    mysql_close(db_connection);
    lr_abort();
}
result_row = (char **)mysql_fetch_row(query_result);
if (result_row == NULL) {
    lr_error_message("没有查询到结果");
    mysql_free_result(query_result);
    mysql_close(db_connection);
    lr_abort();
}
lr_save_string(result_row[0], "paramOrderID");
lr_output_message("Order ID is: %s", lr_eval_string("{paramOrderID}"));
mysql_free_result(query_result);
lr_save_string(lr_eval_string("UPDATE test_data SET status=TRUE, date_used=NOW() WHERE order_id='{paramOrderID}'"),"paramUpdateQuery");
rc = mysql_query(db_connection, lr_eval_string("{paramUpdateQuery}"));
if (rc != 0) {
    lr_error_message("%s", mysql_error(db_connection));
    mysql_close(db_connection);
    lr_abort();
}
rc = mysql_query(db_connection, "COMMIT"); // 提交事务
if (rc != 0) {
    lr_error_message("%s", mysql_error(db_connection));
    mysql_close(db_connection);
    lr_abort();
}