当一次业务处理计算服务和数据库交互较多时，将可能有大量时间浪费在数据传输上，尤其对于计算服务和数据库跨机房或跨地区部署时，浪费的时间会极其可观。为了减少时间浪费可以使用MySQL提供的SQL打包功能。

先来认识两个标记：
CLIENT_MULTI_RESULTS：Tell the server that the client can handle multiple result sets from multiple-statement executions or stored procedures. This flag is automatically enabled if CLIENT_MULTI_STATEMENTS is enabled.
CLIENT_MULTI_STATEMENTS：Tell the server that the client may send multiple statements in a single string (separated by “;”). If this flag is not set, multiple-statement execution is disabled.

接下来通过一个例子了解如何使用MySQL这个功能：

新建表结构：

字段	类型	描述
id	bigint(20) unsigned	自增ID，主键
trans_id	varchar(32)	业务单据号，唯一索引
comments	text	备注

主要代码：

#include <stdio.h>
#include <string.h>
#include "mysql.h"

int main(int argc, const char* argv[])
{
    bool deal_ok = true;

    MYSQL* db_session = 0;

    // init db
    if (deal_ok)
    {
        db_session = mysql_init(db_session);

        if (0 != db_session)
        {
            printf("init db\n");
        }
        else
        {
            deal_ok = false;
            printf(" init db error\n");
        }
    }

    //connect db
    if (deal_ok)
    {
        char db_host[32] = {"127.0.0.1"};
        char db_user[32] = {"test"};
        char db_pass[32] = {"123456789"};
        unsigned long db_port   = 3306;
        unsigned long conn_flag = CLIENT_MULTI_STATEMENTS | CLIENT_REMEMBER_OPTIONS;

        if (mysql_real_connect(db_session, db_host, db_user, db_pass, 0, db_port, 0, conn_flag))
        {
            printf("connect successed\n");
        }
        else
        {
            deal_ok = false;
            printf("connect error: %s\n", mysql_error(db_session));
        }
    }

    //start transaction
    if (deal_ok)
    {
        int db_ret = mysql_query(db_session, "START TRANSACTION");
        if (0 == db_ret)
        {
            printf("start transaction\n");
        }
        else
        {
            deal_ok = false;
            printf("start transaction error: %s\n", mysql_error(db_session));
        }
    }

    //operate db
    if (deal_ok)
    {
        char db_sql[1024] = {0};
        strcat(db_sql, "INSERT INTO test_db.test(trans_id, comments) VALUES(110, 'test');");
        strcat(db_sql, "UPDATE test_db.test SET comments = 'modify' WHERE trans_id = '108';");

        printf("operate db: %s\n", db_sql);

        int db_ret = mysql_real_query(db_session, db_sql, strlen(db_sql));
        if (0 == db_ret)
        {
            while (0 == db_ret)
            {
                printf("    affected rows : %d\n", (int)mysql_affected_rows(db_session));

                db_ret = mysql_next_result(db_session);
            }
        }
        else
        {
            deal_ok = false;
            printf("\terror: %s\n", mysql_error(db_session));
        }
    }

    //complete transaction
    if (0 != db_session)
    {
        if (deal_ok)
        {
            mysql_commit(db_session);
            printf("commit\n");
        }
        else
        {
            mysql_rollback(db_session);
            printf("rollback\n");
        }

        mysql_close(db_session);
    }
    
    return 0;
}