MySQL|Linux下MySQL使用InnoDB引擎笔记 C|Linux

前言:把日常工作以及学习过程中遇到的问题,常记笔记总结我觉得是非常有必要的,不仅可以方便以后在类似过程中遇到同样问题方便查找和解决,也便于其他需要帮助的人们可少找弯路!

一.简介:
1.最近在Linux下使用MySQL数据库时,为了支持事务操作需要用到InnoDB引擎,对于表中处理的插入,更新等操作失败时,回滚前面不应该完成的操作是必须的.

2.一般MySQL默认的数据库引擎是MyISAM,不支持事务和外键,则可使用支持事务和外键的InnoDB引擎.关于如何在Linux下设置MySQL默认引擎InnoDB请参照我前面写的一篇文章小结
http://blog.csdn.net/sunrier/article/details/7475403

3.本笔记着重讲解MySQL的autocommit变量,如何在数据库中设置自动提交,禁止自动提交,如何在对表操作失败后回滚,对表操作成功后提交事务!

二.操作方法
MySQL的autocommit默认是打开的(ON为打开,OFF为关闭或者表示成1为打开,0为关闭)
打开或关闭即是打开自动提交或者关闭自动提交
1.MySQL命令:
方法1:
1.11)如果是支持事务的引擎，如InnoDB则有系统参数设置是否自动commit,查看参数如下：
mysql> show variables like '%autocommit%';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit| ON|
+---------------+-------+
1 row in set (0.01 sec)
mysql>
显示结果为ON,表示事务自动提交,即不用手工去commit。当然,你可以设置其为OFF,然后自己手工去commit。
1.12)打开和关闭自动提交功能命令:
关闭自动提交功能命令
mysql> set session autocommit=OFF;

mysql>
或者
mysql> set session autocommit=off;
Query OK, 0 rows affected (0.00 sec)

mysql>
(注:off不区分大小写)

设置后再次查看:
mysql> show variables like '%autocommit%';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit| OFF|
+---------------+-------+
1 row in set (0.01 sec)
mysql>

可猜测mysql> set session autocommit=on; 应该为打开自动提交功能,不过猜是猜的,最好还是实践下这个命令打开自动提交功能命令
mysql> set session autocommit=ON;

mysql>
设置后再次查看:
mysql> show variables like '%autocommit%';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| autocommit| ON|
+---------------+-------+
1 row in set (0.01 sec)
mysql>
注:如果退出MySQL,下次登陆MySQL后autocommit还会自动设置为默认的变量,这里即autocommit为ON,事务自动提交

方法2:
1.21)如果你在刚才上面方法1.11)中查看参数出现下面的情况:
mysql> show variables like '%autocommit%';
Empty set (0.00 sec)
mysql>
这个情况在我装的虚拟机上就无法查看,然后在公司的服务器上安装的MySQL就没问题(注1.1X为公司的MySQL)。
现在关于为什么会出现两种不同的结果,笔者还没解决这个问题,猜测可能是因为数据库版本的不同可能查看的命令不一样,我最终在网上查找到例外的方法在命令下查看和设置autocommit变量
1.22)查看和设置autocommit变量

查看autocommit变量
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|1 |
+--------------+
1 row in set (0.00 sec)
mysql>
注:autocommit为1表示打开自动提交

设置autocommit变量
mysql> set session autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|0 |
+--------------+
1 row in set (0.00 sec)
mysql>
注:autocommit为0表示关闭自动提交

2.MySQL的配置文件my.cnf:
修改autocommit变量也可以通过修改配置文件my.cnf来关闭autocommit
[mysqld]
init_connect='SET autocommit=0'//在my.cnf文件[mysqld]下面加上这句

3.MySQL数据库程序中使用C的API函数:
切换autocommit模式，ON/OFF:
my_bool mysql_autocommit(MYSQL *mysql, my_bool mode)
如果模式为"1",启用autocommit模式; 如果模式为"0",禁止autocommit模式.
返回值:如果成功返回0; 如果出现错误返回非0值.

回滚当前事务:
my_bool mysql_rollback(MYSQL *mysql)
该函数的动作取决于completion_type系统变量的值.尤其是如果completion_type的值为"2",终结事务后,服务器将执行释放操作,并关闭客户端连接.客户端程序应调用mysql_close(),从客户端一侧关闭连接.
返回值:如果成功返回0; 如果出现错误返回非0值.

提交当前事务:
my_bool mysql_commit(MYSQL *mysql)
该函数的动作受completion_type系统变量的值控制.尤其是如果completion_type的值为2,终结事务并关闭客户端连接后,服务器将执行释放操作.客户端程序应调用mysql_close(),从客户端一侧关闭连接.
返回值:如果成功返回0; 如果出现错误返回非0值.

三.实例说明:
1.MySQL下命令实例(注:student为我的MySQL数据库test中先前已经创建的一个student表信息):
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |24 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
+--------+---------+------+
6 rows in set (0.00 sec)
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|1 |
+--------------+
1 row in set (0.00 sec)
mysql>

从上面可以看出此时数据库autocommit为1也就是自动提交
下面我想插入一个学生信息学号,名字,年龄分别是7,Nicky,22
mysql> insert into student values (7,"Nicky",22);
Query OK, 1 row affected (0.00 sec)
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |24 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
+--------+---------+------+
7 rows in set (0.00 sec)
mysql>
【MySQL|Linux下MySQL使用InnoDB引擎笔记】从MySQL插入命令后,执行查询结果可以看出,刚才插入的一条学生记录(7,"Nicky",22)已经插入到表里面,也许你为了保证执行结果确实是这样,你可能先退出MySQL,再次进入MySQL再查询下,出于这样的本能,我也是这样做的
mysql> exit
Bye
[root@localhost ~]# mysql -uroot -predhat test
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Welcome to the MySQL monitor.Commands end with ; or \g.
Your MySQL connection id is 11 to server version: 5.0.22
Type 'help; ' or '\h' for help. Type '\c' to clear the buffer.
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |24 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
+--------+---------+------+
7 rows in set (0.00 sec)
mysql>
这样可以确信刚才那条学生记录已经确实插入到数据库test的student表里了.
开始主要的环节:
mysql> set session autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|0 |
+--------------+
1 row in set (0.00 sec)
mysql>
从上面可以看出此时数据库变量autocommit已经被设置为0也就是禁止自动提交
下面我想插入一个学生信息学号,名字,年龄分别是8,Jerry,21
mysql> insert into student values (8,"Jerry",21);
Query OK, 1 row affected (0.00 sec)
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |24 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
|8 | Jerry|21 |
+--------+---------+------+
8 rows in set (0.00 sec)
mysql>
从MySQL插入命令后,执行查询结果可以看出,刚才插入的那条学生记录(8,"Jerry",21)也插入到表里面了。
也许你还是为了保证执行结果之外,你可能先退出MySQL,再次进入MySQL再查询下
[root@localhost ~]# mysql -uroot -predhat test
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Welcome to the MySQL monitor.Commands end with ; or \g.
Your MySQL connection id is 12 to server version: 5.0.22
Type 'help; ' or '\h' for help. Type '\c' to clear the buffer.
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |24 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
+--------+---------+------+
7 rows in set (0.00 sec)
mysql>
可以看出刚才那条学生记录(8,"Jerry",21)没有真正插入数据库test的student表里,这应该就是没有自动提交的效果,
说明了刚才设置变量autocommit为0时后来产生了作用。那么现在你也许会想,我现在设置了变量autocommit为0,不自动提交执行结果了,那我应该怎么做才能使我执行的SQL语句还一样对数据库产生影响呢???基于这样的思考和探索下,对于我来说,我刚开始也一无所知,好在现在网络资源强大,我可以利用百度,google等可以利用的资源, 在网上找到了不少相关的知识介绍
发现了下面两个SQL命令:
mysql> rollback;
mysql> commit;
从字面意思上我们可以猜出了它们的大概意思rollback即回滚,commit即提交.现在回到刚才没有插入成功的那条记录那,为了我能够在数据库中变量autocommit设置为0的情况下,执行SQL命令也能对数据库产生影响,那就需要在执行DML的SQL命令后,执行一个commit提交命令
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|1 |
+--------------+
1 row in set (0.00 sec)
mysql> set session autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|0 |
+--------------+
1 row in set (0.00 sec)
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |24 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
+--------+---------+------+
7 rows in set (0.00 sec)
mysql>
上面为重新设置和查看,可以发现autocommit设置为0
mysql> insert into student values (8,"Jerry",21);
Query OK, 1 row affected (0.00 sec)
mysql> commit;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |24 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
|8 | Jerry|21 |
+--------+---------+------+
8 rows in set (0.00 sec)
mysql> exit
Bye
[root@localhost ~]# mysql -uroot -predhat test
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Welcome to the MySQL monitor.Commands end with ; or \g.
Your MySQL connection id is 13 to server version: 5.0.22
Type 'help; ' or '\h' for help. Type '\c' to clear the buffer.
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |24 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
|8 | Jerry|21 |
+--------+---------+------+
8 rows in set (0.00 sec)
mysql>
这样可以确信刚才那条学生记录(8,"Jerry",21)已经确实插入到数据库test的student表里了.
总结:在数据库中autocommit设置为0的情况下,所有的SQL执行命令的结果在遇到commit命令之后才真正提交到数据库中。也许到这会你发现我刚才说了两个SQL命令,到现在只说了commit命令,还有个rollback命令怎么用呢?
继续rollback命令
现在我想把数据库test的student表里名字为"Sunrier"这个小朋友的信息删除了。
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|1 |
+--------------+
1 row in set (0.00 sec)
mysql> set session autocommit=off;
Query OK, 0 rows affected (0.00 sec)
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|0 |
+--------------+
1 row in set (0.00 sec)
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |24 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
|8 | Jerry|21 |
+--------+---------+------+
8 rows in set (0.00 sec)
mysql> delete from student where fname = "Sunrier";
Query OK, 1 row affected (0.01 sec)
mysql> select * from student;
+--------+--------+------+
| studno | fname| age|
+--------+--------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry |30 |
|7 | Nicky|22 |
|8 | Jerry|21 |
+--------+--------+------+
7 rows in set (0.00 sec)
mysql>
从表里面可以看到名字为"Sunrier"的信息删除了,也许你可能马上后悔自己的选择,我找不到任何理由删除"Sunrier",这个小朋友,马上我着急了,我该如何找到该小朋友的原始信息呢,于是你眼前一亮,rollback这个命令,回滚,按照日常的用语是不是回过去的意思.于是你查询了下相关资料,好像可以哎,于是决定自己试试这个SQL命令
mysql> rollback;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |23 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
|8 | Jerry|21 |
+--------+---------+------+
8 rows in set (0.00 sec)
mysql>

为了再次确认,退出MySQL后重新查看
mysql> exit
Bye
[root@localhost ~]# mysql -uroot -predhat test
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Welcome to the MySQL monitor.Commands end with ; or \g.
Your MySQL connection id is 13 to server version: 5.0.22
Type 'help; ' or '\h' for help. Type '\c' to clear the buffer.
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |23 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
|8 | Jerry|21 |
+--------+---------+------+
8 rows in set (0.00 sec)
mysql>

从结果发现,名字为"Sunrier"小朋友的信息又回来了,真是太高兴了.

2.MySQL下使用C的API实例(注:student为我的MySQL数据库test中先前已经创建的一个student表信息):
//dbproc.c

/************************************************************* FileName : dbproc.c FileFunc : MySQL数据库事务操作 Version: V0.1 Author: Sunrier Date: 2012-06-19 Descp: Linux下使用C语言访问MySQL函数 *************************************************************/ #include #include #include #include static MYSQL s_my_connection; static int s_iDbconnected = 0; //数据库连接标志连接时为1,断开时为0int mysql_login(char* pServer,char *pUser,char *pPassword,char *pDataBase) { MYSQL *conn_ptr = NULL; int iRetCode = -1; unsigned int uiTimeOut = 7; if( s_iDbconnected ) return 0; conn_ptr = mysql_init(&s_my_connection); if( !conn_ptr ) { fprintf(stderr,"mysql_init failed ! \n"); return EXIT_FAILURE; } iRetCode = mysql_options(&s_my_connection,MYSQL_OPT_CONNECT_TIMEOUT,(const char *)&uiTimeOut); if( iRetCode) { fprintf(stderr,"MySQL Connection is timeout! \n"); return EXIT_FAILURE; } conn_ptr = NULL; conn_ptr = mysql_real_connect(&s_my_connection,pServer,pUser,pPassword,pDataBase,0,NULL,0); if( conn_ptr ) { printf("MySQL Connection success!\n"); s_iDbconnected = 1; } else { fprintf(stderr,"MySQL Connection failed!\n"); if( mysql_errno(&s_my_connection) ) { fprintf(stderr,"Connection error %d: %s!\n",mysql_errno(&s_my_connection),mysql_error(&s_my_connection)); return EXIT_FAILURE; } } return EXIT_SUCCESS; }void mysql_logout( void ) { if( s_iDbconnected ) mysql_close(&s_my_connection); //关闭连接 s_iDbconnected = 0 ; }//ucMode = 1启动自动模式,一般为默认模式 //ucMode = 0禁止autocommit模式 int mysql_commitmode(unsigned char ucMode) { int iRetCode = -1; iRetCode = mysql_autocommit(&s_my_connection,ucMode); if( iRetCode ) { fprintf(stderr,"Set autocommit %d-mode error ,sqlcode=[%d] : %s ",ucMode,mysql_errno(&s_my_connection),mysql_error(&s_my_connection)); return EXIT_FAILURE; } else { return EXIT_SUCCESS; } } int mysql_proc( void ) { MYSQL *conn_ptr = NULL; MYSQL_RES *res_ptr = NULL; MYSQL_ROW sqlrow; int iTableRow = 0; int iRetCode = 1; char szSql[256]; memset(szSql,0,sizeof(szSql)); sprintf(szSql,"insert into student values(9,'Marry',23)"); iRetCode = mysql_query(&s_my_connection,szSql); if( iRetCode ) { fprintf(stderr,"insert error ,sqlcode=[%d] : %s ",mysql_errno(&s_my_connection),mysql_error(&s_my_connection)); mysql_rollback(&s_my_connection); //回滚操作 return EXIT_FAILURE; } mysql_commit(&s_my_connection); //提交操作(即手动提交) return EXIT_SUCCESS; }

//demo.c

/************************************************************* FileName : demo.c FileFunc : MySQL数据库事务的测试 Version: V0.1 Author: Sunrier Date: 2012-06-19 Descp: Linux下使用C语言访问MySQL函数 *************************************************************/ #include int main(int argc,char *argv[]) { int iRetCode = -1; char szServer[20] = "localhost"; char szUser[20] = "Sunrier"; char szPassword[20] = "redhat" char szDatabase[20] = "test"; iRetCode = mysql_login(szServer,szUser,szPassword,szDatabase); if( iRetCode ) { system("service mysqld start"); iRetCode = mysql_login(szServer,szUser,szPassword,szDatabase); } mysql_commitmode(0); //禁止autocommit模式 iRetCode = mysql_proc(); if( iRetCode ) { printf("MySQL proc error !\n"); } mysql_logout(); return 0; }

//makefile

#makefile all:demo demo:demo.c dbproc.c @gcc -I/usr/include/mysql $?-L/usr/lib/mysql -lmysqlclient-lz -lm -o demo clean: @ls | grep -v ^makefile$$ | grep -v [.]c$$ | grep -v [.]h$$ | grep -v [.]sql$$ | xargs rm -rf #makefile

[Sunrier@localhost MySql]$ ls
dbproc.cdemo.cmakefile
[Sunrier@localhost MySql]$ make
[Sunrier@localhost MySql]$ ls
dbproc.cdemodemo.cmakefile
[Sunrier@localhost MySql]$ ./demo
MySQL Connection success!
[Sunrier@localhost MySql]$
执行前后查看数据库:
由于程序中设置了禁止autocommit模式,如想插入记录成功则需要提交函数,撤消操作则要回滚函数.

执行前数据库:
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |23 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
|8 | Jerry|21 |
+--------+---------+------+
8 rows in set (0.00 sec)

执行后数据库:
mysql> select * from student;
+--------+---------+------+
| studno | fname| age|
+--------+---------+------+
|1 | Jack|67 |
|2 | Tim|22 |
|3 | Sunrier |23 |
|4 | Helen|26 |
|5 | Tony|29 |
|6 | Cherry|30 |
|7 | Nicky|22 |
|8 | Jerry|21 |
|9 | Marry|23 |
+--------+---------+------+
9 rows in set (0.00 sec)
mysql>

//student.sql

drop database if exists test; create database test; use test; create table student ( studno integer auto_increment not null primary key, fname varchar(30), age integer ); -- )engine=innodb charset=gb2312; --insert into student values ('',"Sunrier",22); --insert into student values ('',"Tom",23); --insert into student values ('',"Jerry",21);