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(); 
}

// 再次查找数据,应该为空了,因为前面的事务更新了标志 
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(); 

result_row = (char **)mysql_fetch_row(query_result); 
if (result_row == NULL) { 
    lr_output_message("Result set is empty as expected"); 
    mysql_free_result(query_result); 
} else { 
    lr_error_message("Did not expect the result set to contain any rows"); 
    mysql_free_result(query_result); 
    mysql_close(db_connection); 
    lr_abort(); 
}