欢迎进入Linux社区论坛,与200万技术人员互动交流 >>进入 这里顺带解释一下什么是non-interactive connection Non-Interactive Commands Just do a quick look up on a table without logging into the client, running the query then logging back out aga
欢迎进入Linux社区论坛,与200万技术人员互动交流 >>进入
这里顺带解释一下什么是non-interactive connection
> Non-Interactive Commands
Just do a quick look up on a table without logging into the client, running the query then logging back out again.
You can instead just type one line using the ' -e ' flag.
[sql]
c:\mysql\bin\mysql -u admin -p myDatabase -e 'SELECT * FROM employee'
net_read_timeout / net_write_timeout
The number of seconds to wait for more data from a connection before aborting the read. Before MySQL 5.1.41, this timeout applies only to TCP/IP connections, not to connections made through Unix socket files, named pipes, or shared memory. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort. When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort. See also slave_net_timeout.
On Linux, the NO_ALarm build flag affects timeout behavior as indicated in the description of the net_retry_count system variable.
解释:这个参数只对TCP/IP链接有效,分别是数据库等待接收客户端发送网络包和发送网络包给客户端的超时时间,这是在Activity状态下的线程才有效的参数
JDBC setQueryTimeout函数:
为了避免查询出现死循环,或时间过长等现象,而导致线程阻塞,在获得Statement的实例后,stmt.setQueryTimeout(10); 避免因为查询导致程序出现线程阻塞。
但昨天发现程序出现了,“ORA-01013: 用户请求取消当前的操作”的异常。手工执行出错SQL语句发现,这个语句耗时20多秒。因为setQueryTimeout(10),所以还没有执行完查询语句就抛出异常了。使用setQueryTimeout(10)时一定要把时间设置的长一些,如60秒以上。只要不导致线程长期阻塞,就可以。太短了容易抛出,“ORA-01013: 用户请求取消当前的操作”的异常
JDBC实现setQueryTimeout的原理:
[java]
class IfxCancelQueryImpl extends TimerTask
implements IfmxCancelQuery
{
IfxStatement stmt;
Timer t = null;
public void startCancel(IfxStatement paramIfxStatement, int paramInt)
throws Exception
{
this.stmt = paramIfxStatement;
this.t = new Timer(true);
this.t.schedule(this, paramInt * 1000);
}
public void run()
{
try
{
this.stmt.cancel();
this.t.cancel();
}
catch (SQLException localSQLException)
{
this.t.cancel();
throw new Error(localSQLException.getErrorCode() + ":" + localSQLException.getMessage());
}
}
}
可见,query timeout是通过客户端解决方案来做的,服务器端无需知晓。通过一个timer线程来监控执行时间,如果执行时间超时,则会schedule run()函数。
[1] [2]

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方法:1、利用right函数,语法为“update 表名 set 指定字段 = right(指定字段, length(指定字段)-1)...”;2、利用substring函数,语法为“select substring(指定字段,2)..”。

mysql的msi与zip版本的区别:1、zip包含的安装程序是一种主动安装,而msi包含的是被installer所用的安装文件以提交请求的方式安装;2、zip是一种数据压缩和文档存储的文件格式,msi是微软格式的安装包。

在mysql中,可以利用char()和REPLACE()函数来替换换行符;REPLACE()函数可以用新字符串替换列中的换行符,而换行符可使用“char(13)”来表示,语法为“replace(字段名,char(13),'新字符串') ”。

转换方法:1、利用cast函数,语法“select * from 表名 order by cast(字段名 as SIGNED)”;2、利用“select * from 表名 order by CONVERT(字段名,SIGNED)”语句。

本篇文章给大家带来了关于mysql的相关知识,其中主要介绍了关于MySQL复制技术的相关问题,包括了异步复制、半同步复制等等内容,下面一起来看一下,希望对大家有帮助。

本篇文章给大家带来了关于mysql的相关知识,其中主要介绍了mysql高级篇的一些问题,包括了索引是什么、索引底层实现等等问题,下面一起来看一下,希望对大家有帮助。

在mysql中,可以利用REGEXP运算符判断数据是否是数字类型,语法为“String REGEXP '[^0-9.]'”;该运算符是正则表达式的缩写,若数据字符中含有数字时,返回的结果是true,反之返回的结果是false。


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