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DBCP配置(�?

Masen — Sat, 27 Feb 2016 03:06:00 GMT

DBCP�q�接池介�l?/h1>
-----------------------------
目前 DBCP 有两个版本分别是 1.3 �?1.4�?/p>
DBCP 1.3 版本需要运行于 JDK 1.4-1.5 �Q�支�?JDBC 3�?/p>
DBCP 1.4 版本需要运行于 JDK 1.6 �Q�支�?JDBC 4�?/p>
1.3�?.4��Z��同一套源代码�Q�含有所有的bug修复和新�Ҏ��。因此在选择DBCP版本的时候，要看你用的是什么JDK版本�?/p>
DBCP1.2版本性能一般，比c3p0差挺多。DBCP1.4�?.3�Q�配合（依赖�Q�commons pool 1.6的jar�?各方面功能、性能推进到新的高峰。相�?.2版本提高不少。超��?或相�?了c3p0.��使用DBCP1.4�?.3 + commons pool 1.6

Tomcat7 中保留DBCP�q�接池，以兼容已有应用。�ƈ提供了新的Tomcat JDBC pool作�ؓDBCP的可选替代。新出的Tomcat JDBC pool�Q�据说比DBCP 1.4要好�Q�未接触�Q�也不在本文讨论范围内�?/p>

DBCP�q�接池配�|�参数讲�?/h1>
-----------------------------
一、Apache官方DBCP文档�l�出的配�|�示例：
可参见：http://tomcat.apache.org/tomcat-6.0-doc/jndi-datasource-examples-howto.html

maxActive="100" maxIdle="30" maxWait="10000"
username="javauser" password="javadude" driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/javatest"/>

tomcat JDBC�q�接池配�|�示例，自动��查连接的可用性，dbcp定时��连接，dbcp自动重连的配�|?/strong>
Xml代码
<Resource
name="jdbc/TestDB"  JNDI数据源的name�Q�查找时用：java:comp/env/jdbc/TestDB
type="javax.sql.DataSource"
factory="org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory"
driverClassName="com.mysql.jdbc.Driver" JDBC驱动�c?nbsp;
url="jdbc:mysql://localhost:3306/test?
characterEncoding=UTF-8&autoReconnectForPools=true&rewriteBatchedStatements=true&useCursorFetch=true&defaultFetchSize=20" 数据库URL地址
username="xxx" 讉K��数据库用户名
password="xxx" 讉K��数据库的密码

maxWait="3000" 从池中取�q�接的最大等待时��_��单位ms.
initialSize="10"  初始化连�?nbsp;
maxIdle="60"   最大空闲连�?nbsp;
minIdle="10"   最��空闲连�?nbsp;
maxActive="80" 最大活动连�?nbsp;

validationQuery = "SELECT 1"  验证使用的SQL语句
testWhileIdle = "true"      指明�q�接是否被空闲连接回收器(如果�?�q�行��?如果��失�?则连接将被从池中去除.
testOnBorrow = "false"   借出�q�接时不要测试，否则很媄响性能
timeBetweenEvictionRunsMillis = "30000"  �?0�U�运行一�ơ空闲连接回收器
minEvictableIdleTimeMillis = "1800000"  池中的连接空�?0分钟后被回收
numTestsPerEvictionRun="10" 在每�ơ空闲连接回收器�U�程(如果�?�q�行时检查的�q�接数量

removeAbandoned="true"  �q�接泄漏回收参数�Q�当可用�q�接数少�?个时才执�?nbsp;
removeAbandonedTimeout="180"  �q�接泄漏回收参数�Q?80�U�，泄露的连接可以被删除的超时�?nbsp;
/>

DBCP�q�接池的自我��?/h1>
-----------------------------
默认配置的DBCP�q�接池，是不�Ҏ��中的�q�接做测试的�Q�有时连接已断开了，但DBCP�q�接池不知道�Q�还以�ؓ�q�接是好的呢�?/p>
应用从池中取��L��q�接讉K��数据库一定会报错。这也是好多��Z��喜欢DBCP的原因�?/p>

问题例一�Q?/p>
MySQL8��时问题�Q�Mysql服务器默认连接的“wait_timeout”�?��时�Q�也��是说一个connection�I�闲��过8个小�Ӟ��Mysql��自动断开�?connection�?/p>
但是DBCP�q�接池�ƈ不知道连接已�l�断开了，如果�E�序正��y使用到这个已�l�断开的连接，�E�序��׃��报错误�?/p>

问题例二�Q?/p>
以前�q��用Sybase数据库，�׃��某种原因�Q�数据库��M��后重启、或断网后恢复�?/p>
�{�了�U?0分钟后，DBCP�q�接池中的连接还都是不能使用的（断开的）�Q�访问数据应用一直报错，最后只能重启Tomcat问题才解�?�?/p>

解决�Ҏ��Q?/p>
�Ҏ��1、定时对�q�接做测试，��试��p�|��关闭连接�?/p>
�Ҏ��2、控制连接的�I�闲旉��辑ֈ�N分钟�Q�就关闭�q�接�Q�（然后可再新徏�q�接�Q��?/p>
以上两个�Ҏ��使用��L��一个就可以解决以述两类问题。如果只使用�Ҏ��2�Q�徏�?N <= 5分钟。连接断开后最�?分钟后可恢复�?/p>
也可混合使用两个�Ҏ��Q�徏�?N = 30分钟�?/p>

下面��是DBCP�q�接池，同时使用了以上两个方案的配置配置
validationQuery = "SELECT 1" 验证�q�接是否可用�Q��用的SQL语句
testWhileIdle = "true" 指明�q�接是否被空闲连接回收器(如果�?�q�行��?如果��失�?则连接将被从池中去除.
testOnBorrow = "false" 借出�q�接时不要测试，否则很媄响性能
timeBetweenEvictionRunsMillis = "30000" �?0�U�运行一�ơ空闲连接回收器
minEvictableIdleTimeMillis = "1800000" 池中的连接空�?0分钟后被回收,默认值就�?0分钟�?/p>
numTestsPerEvictionRun="3" 在每�ơ空闲连接回收器�U�程(如果�?�q�行时检查的�q�接数量�Q�默认值就�?.

解释�Q?/p>
配置timeBetweenEvictionRunsMillis = "30000"后，�?0�U�运行一�ơ空闲连接回收器�Q�独立线�E�）。�ƈ每次��?个连接，如果�q�接�I�闲旉��过30分钟��销毁。销毁连接后�Q�连接数量就��了�Q�如果小于minIdle数量�Q�就新徏�q�接�Q�维护数量不��于minIdle�Q�过行了新老更�ѝ�?/p>
testWhileIdle = "true" 表示�?0�U�，取出3条连接，使用validationQuery = "SELECT 1" 中的SQL�q�行��试 �Q�测试不成功��销毁连接。销毁连接后�Q�连接数量就��了�Q�如果小于minIdle数量�Q�就新徏�q�接�?/p>
testOnBorrow = "false" 一定要配置�Q�因为它的默认值是true。false表示每次从连接池中取��接时�Q�不需要执行validationQuery = "SELECT 1" 中的SQL�q�行��试。若配置为true,�Ҏ��能有非常大的媄响，性能会下�?-10倍。所在一定要配置为false.
�?0�U�，取出numTestsPerEvictionRun条连接（本例�?�Q�也是默认��|��Q�发�?SELECT 1" SQL语句�q�行��试 �Q�测试过的连接不��是“被��?#8221;了，�q�算是空闲的。连接空�?0分钟后会被销毁�?/p>


DBCP�q�接池配�|�参数注意事��?
-----------------------------
maxIdle��g��maxActive值应配置的接�q��?/p>
因�ؓ�Q�当�q�接数超�q�maxIdle值后�Q�刚刚��用完的连接（刚刚�I�闲下来�Q�会立即被销毁。而不是我惌��的空闲M�U�后再销毁�v一个缓冲作用。这一点DBCP做的可能与你惛_��的不一栗��?/p>
若maxIdle与maxActive相差较大�Q�在高负载的�pȝ��中会��D��频繁的创建、销毁连接，�q�接数在maxIdle与maxActive间快速频�J��L动，�q�不是我惌��的�?/p>
高负载系�l�的maxIdle值可以设�|��ؓ与maxActive相同或设�|��ؓ-1(-1表示不限�?�Q�让�q�接数量在minIdle与maxIdle间缓冲慢速�L动�?/p>

timeBetweenEvictionRunsMillis��讄��?/p>
initialSize="5"�Q�会在tomcat一启动�Ӟ��创徏5条连接，效果很理惟�?/p>
但同时我们还配置了minIdle="10"�Q�也��是��_��最��要保持10条连接，那现在只�?条连接，哪什么时候再创徏��的5条连接呢�Q?/p>
1、等业务压力上来了， DBCP��׃��创徏新的�q�接�?/p>
2、配�|�timeBetweenEvictionRunsMillis=“旉��”,DBCP会启用独立的工作�U�程定时��查，补上��的5条连接。销毁多余的�q�接也是同理�?/p>

�q�接销毁的逻辑
------------------------------
DBCP的连接数会在 0 - minIdle - maxIdle - maxActive 之间变化。变化的逻辑描述如下�Q?/p>

默认未配�|�initialSize(默认值是0)和timeBetweenEvictionRunsMillis参数�Ӟ��刚启动tomcat�Ӟ��q�接数是0。当应用有一个�ƈ发访问数据库时DBCP创徏一个连接�?/p>
目前�q�接数量�q�未辑ֈ�minIdle�Q�但DBCP也不自动创徏新连接已使数量达到minIdle数量�Q�没有一个独立的工作�U�程来检查和创徏�Q��?/p>
随着应用�q�发讉K��数据库的增多�Q�连接数也增多，但都与minIdle值无养I��很快minIdle被超��，minIdle��g��点用都没有�?/p>
直到�q�接的数量达到maxIdle��|��q�时的连接都是只增不减的�?再��l�发展，�q�接数再增多�q�超�q�maxIdle�Ӟ��使用完的�q�接�Q�刚刚空闲下来的�Q�会立即关闭�Q��M��q�接的数量稳定在maxIdle但不会超�q�maxIdle�?/p>
但活动连接（在��用中的连接）可能数量上瞬间超�q�maxIdle�Q�但永远不会��过maxActive�?/p>
�q�时如果应用业务压力��了�Q�访问数据库的�ƈ发少了，�q�接��C��不会减少�Q�没有一个独立的�U�程来检查和销毁）�Q�将保持在maxIdle的数量�?/p>

默认未配�|�initialSize(默认值是0)�Q�但配置了timeBetweenEvictionRunsMillis=“30000”�Q?0�U�）参数�Ӟ��刚启动tomcat�Ӟ��q�接数是0。马上应用有一个�ƈ发访问数据库时DBCP创徏一个连接�?/p>
目前�q�接数量�q�未辑ֈ�minIdle�Q�每30�U�DBCP的工作线�E�检查连接数是否��于minIdle数量�Q�若��于��创建新�q�接直到辑ֈ�minIdle数量�?/p>
随着应用�q�发讉K��数据库的增多�Q�连接数也增多，直到辑ֈ�maxIdle倹{��这期间�?0�U�DBCP的工作线�E�检查连接是否空闲了30分钟�Q�若是就销毁。但此时是业务的高峰期，是不会有长达30分钟的空闲连接的�Q�工作线�E�查了也是白查，但它在工作。到�q�里�q�接数量一直是呈现增长的趋�ѝ�?/p>
当连接数再增多超�q�maxIdle�Ӟ��使用完的�q�接(刚刚�I�闲下来)会立卛_��闭，��M��q�接的数量稳定在maxIdle。停止了增长的趋�ѝ��但�z�d��q�接�Q�在使用中的�q�接�Q�可能数量上瞬间��过maxIdle�Q�但永远不会��过maxActive�?/p>
�q�时如果应用业务压力��了�Q�访问数据库的�ƈ发少了，�?0�U�DBCP的工作线�E�检查连�?默认每次�?�?是否�I�闲辑ֈ�30分钟(�q�是默认�?�Q�若�q�接�I�闲辑ֈ�30分钟�Q�就销毁连接。这时连接数减少了，呈下降趋势，��从maxIdle走向minIdle。当��于minIdle值时�Q�则DBCP创徏新连接已使数量稳定在minIdle�Q��ƈ�q�行着新老更�ѝ�?/p>

配置initialSize=“10”�Ӟ��tomcat一启动��创�?0条连接。其它同上�?/p>

minIdle要与timeBetweenEvictionRunsMillis配合使用才有�?单独使用minIdle不会起作用�?/p>

Tomcat中配�|�DBCP�q�接�?/h1>
-----------------------------
Tomcat自带DBCP的包�Q�是$CATALINA_HOME/lib/tomcat-dbcp.jar�?/p>
tomcat-dbcp.jar含有commons pool、commons DBCP两个包的内容。但只含有与�q�接池有关的�c�R�?/p>
数据源配�|�在context.xml文�g中，要在tomcat的lib目录中放jdbc 驱动�?/p>
数据源配�|�在server.xml的host中，不需要在tomcat的lib目录中放jdbc 驱动包，只��用工�E�中的jdbc驱动�?/p>

JNDI配置:更改tomcat的server.xml或context.xml

全局的数据源�Q?/p>
如果需要配�|�全局�?Resource�Q�则在server.xml的GlobalNamingResources节点里加入Resource�Q�再在Context节点里加入ResourceLink的配�|��?/p>
全局的resource只是��Z��重用�Q�方便所有该tomcat下的web工程的数据源��理�Q�但如果你的tomcat不会同时加蝲多个web工程�Q�也��是说一个tomcat只加载一个web工程�Ӟ��是没有必要配�|�全局的resource的�?/p>

每个web工程一个数据源�Q?/p>
�?CATALINA_HOME/conf/context.xml的根节点Context里加入Resource配置。这�U�配�|�方法，你在context.xml配置了一个数据源�Q�但Tomcat中有同时�q�行着5个工�E�，那了��坏事儿了，�q�个在Tomcat启动时数据源被创��Z��5份，每个工程1份数据源。连接数会是你配�|�的参数�?倍�?/p>
只有在你的Tomcat只加载一个web工程�?才可以直接以context.xml配置数据源�?/p>

type="javax.sql.DataSource" //数据源类型，使用标准的javax.sql.DataSource
driverClassName="com.mysql.jdbc.Driver" //JDBC驱动�?nbsp;
url="jdbc:mysql://localhost:3306/test" //数据库URL地址
username="test" //数据库用户名
password="test" //数据库密�?/p>
maxIdle="40" //最大的�I�闲�q�接�?/p>
maxWait="4000" //当池的数据库�q�接已经被占用的时候，最大等待时�?/p>
maxActive="40" //�q�接池当中最大的数据库连�?/p>
removeAbandoned="true"
removeAbandonedTimeout="180"
logAbandoned="true" //被丢弃的数据库连接是否做记录�Q�以便跟�t?/p>
factory="org.apache.tomcat.dbcp.dbcp.BasicDataSourceFactory" />

�q�里的factory指的是该Resource 配置使用的是哪个数据源配�|�类�Q�这里��用的是tomcat自带的标准数据源Resource配置�c�，�q�个�c�M��可以自己写，实现javax.naming.spi.ObjectFactory 接口卛_��。某些地方��用的commons-dbcp.jar中的org.apache.commons.dbcp.BasicDataSourceFactory�Q�如果��用这个就需把commons-dbcp.jar及其依赖的jar包，都放在tomcat的lib下，光放在工�E�的WEB-INF/lib下是不够的�?/p>

ResourceLink 的配�|�有多种�Q?/p>

1)tomcat安装目录下的conf/context.xml�Q�把全局的resource直接公开�l�该tomcat下的所有web工程�Q�在Context节点中加入：

不徏议在此文件中�Q�不使用�Q�而��?lt;Resource/>直接配置数据源，原因上面已说明了�?

2)tomcat安装目录下的conf/server.xml�Q�该�Ҏ��可以指定把哪些source�l�定到哪个web工程下�?/p>

也可在此文�g中，不��?lt;ResourceLink/>�Q�而��?lt;Resource/>直接配置数据源�?/p>

3)安装目录下的conf/localhost/下徏立一个xml文�g�Q�文件名�?lt;yourAppName>.xml。比如工�E�名为test�Q�则该xml名�ؓtest.xml�?/p>


也可在此文�g中，不��?lt;ResourceLink/>�Q�而��?lt;Resource/>直接配置数据源�?/p>

4)tomcat安装目录下的\webapps\test\META-INF\context.xml的Context节点中增�?
也可在此文�g中，不��?lt;ResourceLink/>�Q�而��?lt;Resource/>直接配置数据源�?/p>

本文内容都在tomcat6.0上运行测试过�Q�还下蝲了commons DBCP的源码，加入了跟�t�日志，用于验证本文的理论�?/p>

�q�接池排名（�U�个人看法）
-----------------------------
Tomcat JDBC pool
DBCP 1.4
c3p0 速度不错
BoneCP 速度不错�Q�但会启用很多附加线�E�做回收、关闭工作�?/p>
Proxool 在高�q�发时出现异�?/p>
DBCP 1.2
DBPool 最差，垫底�?/p>
参考文档《Java�q�接池评估报告�?/p>

Masen 2016-02-27 11:06 发表评论

Masen — Sun, 12 Apr 2015 11:34:00 GMT

防止mysql重复插入记录的方法有很多�U�，常用的是ignore,Replace,ON DUPLICATE KEY UPDATE,当然我们也可以在php中加以判断了�?/div>
�Ҏ��一�Q��用ignore关键�?/span>
如果是用主键primary或者唯一索引unique区分了记录的唯一�?避免重复插入记录可以使用�Q?/p>
代码如下:
代码如下复制代码
INSERT IGNORE INTO `table_name` (`email`, `phone`, `user_id`) VALUES ('test9@163.com', '99999', '9999');

�q�样当有重复记录��׃��忽略,执行后返回数�?

�q�有个应用就是复制表,避免重复记录�Q?nbsp;
代码如下:
代码如下复制代码
INSERT IGNORE INTO `table_1` (`name`) SELECT `name` FROM `table_2`;

�Ҏ��二：使用Replace

语法格式�Q?/p>
代码如下:
代码如下复制代码
REPLACE INTO `table_name`(`col_name`, ...) VALUES (...);
REPLACE INTO `table_name` (`col_name`, ...) SELECT ...;
REPLACE INTO `table_name` SET `col_name`='value',
...��法说明�Q?/p>
REPLACE的运行与INSERT很相�?但是如果旧记录与新记录有相同的��|��则在新记录被插入之前�Q�旧记录被删除，卻I��

��试把新行插入到表中
当因为对于主键或唯一关键字出现重复关键字错误而造成插入��p�|�Ӟ��
从表中删除含有重复关键字值的冲突�?nbsp;
再次��试把新行插入到表中
旧记录与新记录有相同的值的判断标准��是�Q?br />表有一个PRIMARY KEY或UNIQUE索引�Q�否则，使用一个REPLACE语句没有意义。该语句会与INSERT相同�Q�因为没有烦引被用于��定是否新行复制了其它的行�?nbsp;
�q�回��|��
REPLACE语句会返回一个数�Q�来指示受媄响的行的数目。该数是被删除和被插入的行数的和
受媄响的行数可以�Ҏ��地确定是否REPLACE只添加了一行，或者是否REPLACE也替换了其它行：��查该数是否�ؓ1�Q�添加）或更大（替换�Q��?nbsp;
�C�Z��:
# eg:(phone字段为唯一索引)
代码如下:
代码如下复制代码
REPLACE INTO `table_name` (`email`, `phone`, `user_id`) VALUES ('test569', '99999', '123');
另外,�?SQL Server 中可以这样处理：

代码如下:
代码如下复制代码
if not exists (select phone from t where phone= '1')   insert into t(phone, update_time) values('1', getdate()) else    update t set update_time = getdate() where phone= '1'
�Ҏ��三：ON DUPLICATE KEY UPDATE

�?#8205;上所写，你也可以在INSERT INTO…..后面加上 ON DUPLICATE KEY UPDATE�Ҏ��来实现。如果您指定了ON DUPLICATE KEY UPDATE�Q��ƈ且插入行后会��D��在一个UNIQUE索引或PRIMARY KEY中出现重复��|��则执行旧行UPDATE�?nbsp;
例如�Q�如果列a被定义�ؓUNIQUE�Q��ƈ且包含�?�Q�则以下两个语句��h��相同的效果：

代码如下:
代码如下复制代码

INSERT INTO `table` (`a`, `b`, `c`) VALUES (1, 2, 3) ON DUPLICATE KEY UPDATE `c`=`c`+1;
UPDATE `table` SET `c`=`c`+1 WHERE `a`=1;
如果行作为新记录被插入，则受影响行的��gؓ1�Q�如果原有的记录被更斎ͼ�则受影响行的��gؓ2�?/p>

注释�Q�如果列b也是唯一列，则INSERT与此UPDATE语句相当�Q?nbsp;
代码如下:
代码如下复制代码
UPDATE `table` SET `c`=`c`+1 WHERE `a`=1 OR `b`=2 LIMIT 1;
如果a=1 OR b=2与多个行向匹配，则只有一个行被更新。通常�Q�您应该��量避免对带有多个唯一关键字的表��用ON DUPLICATE KEY子句�?/p>

您可以在UPDATE子句中��用VALUES(col_name)函数从INSERT…UPDATE语句的INSERT部分引用列倹{��换句话��_��如果没有发生重复关键字冲�H�，则UPDATE子句中的VALUES(col_name)可以引用被插入的col_name的倹{��本函数特别适用于多行插入。VALUES()函数只在INSERT…UPDATE语句中有意义�Q�其它时候会�q�回NULL�?/p>

代码如下:
代码如下复制代码
INSERT INTO `table` (`a`, `b`, `c`) VALUES (1, 2, 3), (4, 5, 6) ON DUPLICATE KEY UPDATE `c`=VALUES(`a`)+VALUES(`b`);
本语句与以下两个语句作用相同�Q?/p>

代码如下:
代码如下复制代码
INSERT INTO `table` (`a`, `b`, `c`) VALUES (1, 2, 3) ON DUPLICATE KEY UPDATE `c`=3;
INSERT INTO `table` (`a`, `b`, `c`) VALUES (4, 5, 6) ON DUPLICATE KEY UPDATE c=9;
注释�Q�当您��用ON DUPLICATE KEY UPDATE�Ӟ��DELAYED选项被忽略�?/p>

�C�Z��Q?/p>
�q�个例子是我在实际项目中用到的：是将一个表的数据导入到另外一个表中，数据的重复性就得考虑(如下)�Q�唯一索引为：email�Q?/p>

代码如下:
代码如下复制代码
INSERT INTO `table_name1` (`title`, `first_name`, `last_name`, `email`, `phone`, `user_id`, `role_id`, `status`, `campaign_id`)
    SELECT '', '', '', `table_name2`.`email`, `table_name2`.`phone`, NULL, NULL, 'pending', 29 FROM `table_name2`
    WHERE `table_name2`.`status` = 1
ON DUPLICATE KEY UPDATE `table_name1`.`status`='pending'
再脓一个例子：

代码如下:
代码如下复制代码
INSERT INTO `class` SELECT * FROM `class1` ON DUPLICATE KEY UPDATE `class`.`course`=`class1`.`course`
其它关键�Q�DELAYED 做�ؓ快速插入，�q�不是很兛_��失效性，提高插入性能�?nbsp;
IGNORE 只关注主键对应记录是不存在，无则��d��Q�有则忽略�?/p>
php防止重复插入记录实例
代码如下复制代码

$link=mysql_connect(‘localhost’,’root’,’1234’); //得到MySQL数据�?/a>�q�接
$username=$_GET["name"]; //得到从客��L��表单传过来的数据
$q="select * from usertable where user_name='$username'";
mysql_query("SET NAMES gb2312"); //避免出现中文��q��
$rs = mysql_query($q, $link); //查询数据�?/a>
$num_rows = mysql_num_rows($rs); //得到查询�l�果的总行�?nbsp;
if($num_rows==0)
// 烈火? liehuo.net �Ƣ迎复制,拒绝恶意采集ｌｉｅｈｕｏ�Q�ｎｅｔ
{
$exec="insert into student (user_name) values ($username)";
mysql_query("SET NAMES gb2312");
mysql_query($exec, $link); //若没有此用户则将数据插入到数据库(注册用户)
echo "用户注册成功�Q?;
}
else
{
echo "该用户名已存在，请重新选择用户名！";
}
?>

附一些删除重复记录的�Ҏ��
查询及删除重复记录的SQL语句
1、查找表中多余的重复记录�Q�重复记录是�Ҏ��单个字段�Q�peopleId�Q�来判断
代码如下复制代码
select * from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
2、删除表中多余的重复记录�Q�重复记录是�Ҏ��单个字段�Q�peopleId�Q�来判断�Q�只留有rowid最��的记录
代码如下复制代码
delete from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)
3、查找表中多余的重复记录�Q�多个字�D�）
代码如下复制代码
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
4、删除表中多余的重复记录�Q�多个字�D�）�Q�只留有rowid最��的记录
代码如下复制代码
delete from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
5、查找表中多余的重复记录�Q�多个字�D�）�Q�不包含rowid最��的记录
代码如下复制代码
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)

Masen 2015-04-12 19:34 发表评论

Masen — Sat, 11 Apr 2015 11:00:00 GMT
     摘要: ��Z��么要分表和分区？日常开发中我们�l�常会遇到大表的情况�Q�所谓的大表是指存储了百万��乃至千万�U�条记录的表。这��L��表过于庞大，��D��数据库在查询和插入的时候耗时太长�Q�性能低下�Q�如果涉及联合查询的情况�Q�性能会更加糟�p�。分表和表分区的目的��是减少数据库的负担�Q�提高数据库的效率，通常�Ҏ��讲就是提高表的增删改查效率。什么是分表�Q�分表是��一个大表按照一定的规则分解成多张具有独立存储空间的实体表，我们可以�U�Cؓ子表�Q?..  阅读全文

Masen 2015-04-11 19:00 发表评论

Masen — Mon, 02 Aug 2010 09:25:00 GMT

�W�一�?日志��理
1.forcing log switches   �q��开��x��?br /> sql> alter system switch logfile;
2.forcing checkpoints    ��?br /> sql> alter system checkpoint;
3.adding online redo log groups    加入联机重做日志�l?br /> sql> alter database add logfile [group 4]
sql> ('/disk3/log4a.rdo','/disk4/log4b.rdo') size 1m;
4.adding online redo log members    加入联机重做日志成员
sql> alter database add logfile member
sql> '/disk3/log1b.rdo' to group 1,
sql> '/disk4/log2b.rdo' to group 2;
5.changes the name of the online redo logfile     更改名称的联机重做日�?br /> sql> alter database rename file 'c:/oracle/oradata/oradb/redo01.log'
sql> to 'c:/oracle/oradata/redo01.log';
6.drop online redo log groups    落在�U�K��做日志组
sql> alter database drop logfile group 3;
7.drop online redo log members       落在�U�K��做日志成�?br /> sql> alter database drop logfile member 'c:/oracle/oradata/redo01.log';
8.clearing online redo log files �l�算在线重做日志文�g
sql> alter database clear [unarchived] logfile 'c:/oracle/log2a.rdo';
9.using logminer analyzing redo logfiles 使用logminer分析重做日志
a. in the init.ora specify utl_file_dir = ' '
b. sql> execute dbms_logmnr_d.build('oradb.ora','c:\oracle\oradb\log');
c. sql> execute dbms_logmnr_add_logfile('c:\oracle\oradata\oradb\redo01.log',
sql> dbms_logmnr.new);
d. sql> execute dbms_logmnr.add_logfile('c:\oracle\oradata\oradb\redo02.log',
sql> dbms_logmnr.addfile);
e. sql> execute dbms_logmnr.start_logmnr(dictfilename=>'c:\oracle\oradb\log\oradb.ora');
f. sql> select * from v$logmnr_contents(v$logmnr_dictionary,v$logmnr_parameters
sql> v$logmnr_logs);
g. sql> execute dbms_logmnr.end_logmnr;

�W�二�?表空间管�?br /> 1.create tablespaces   创徏表空�?br /> sql> create tablespace tablespace_name datafile 'c:\oracle\oradata\file1.dbf' size 100m,
sql> 'c:\oracle\oradata\file2.dbf' size 100m minimum extent 550k [logging/nologging]
sql> default storage (initial 500k next 500k maxextents 500 pctinccease 0)
sql> [online/offline] [permanent/temporary] [extent_management_clause]
2.locally managed tablespace    本地��理表空�?br /> sql> create tablespace user_data datafile 'c:\oracle\oradata\user_data01.dbf'
sql> size 500m extent management local uniform size 10m;
3.temporary tablespace    临时表空�?br /> sql> create temporary tablespace temp tempfile 'c:\oracle\oradata\temp01.dbf'
sql> size 500m extent management local uniform size 10m;
4.change the storage setting    改变存储讄��
sql> alter tablespace app_data minimum extent 2m;
sql> alter tablespace app_data default storage(initial 2m next 2m maxextents 999);
5.taking tablespace offline or online    同时表空间离�U�或在线
sql> alter tablespace app_data offline;
sql> alter tablespace app_data online;
6.read_only tablespace    只读表空�?br /> sql> alter tablespace app_data read only|write;
7.droping tablespace    删除表空�?br /> sql> drop tablespace app_data including contents;
8.enableing automatic extension of data files   enableing自动廉��数据档案
sql> alter tablespace app_data add datafile 'c:\oracle\oradata\app_data01.dbf' size 200m
sql> autoextend on next 10m maxsize 500m;
9.change the size fo data files manually ��寸变化的数据档案手�?br /> sql> alter database datafile 'c:\oracle\oradata\app_data.dbf' resize 200m;
10.Moving data files: alter tablespace �U�d��数据档案:改变表空�?br /> sql> alter tablespace app_data rename datafile 'c:\oracle\oradata\app_data.dbf'
sql> to 'c:\oracle\app_data.dbf';
11.moving data files:alter database   �U�d��数据档案:改变数据�?br /> sql> alter database rename file 'c:\oracle\oradata\app_data.dbf'
sql> to 'c:\oracle\app_data.dbf';

�W�三�?�?br /> 1.create a table   新徏�?br /> sql> create table table_name (column datatype,column datatype]....)
sql> tablespace tablespace_name [pctfree integer] [pctused integer]
sql> [initrans integer] [maxtrans integer]
sql> storage(initial 200k next 200k pctincrease 0 maxextents 50)
sql> [logging|nologging] [cache|nocache]
2.copy an existing table   复制一个现有的�?br /> sql> create table table_name [logging|nologging] as subquery
3.create temporary table   创徏临时�?br /> sql> create global temporary table xay_temp as select * from xay;
on commit preserve rows/on commit delete rows
4.pctfree = (average row size - initial row size) *100 /average row size
pctused = 100-pctfree- (average row size*100/available data space)
5.change storage and block utilization parameter 改变存储和利用块参数
sql> alter table table_name pctfree=30 pctused=50 storage(next 500k
sql> minextents 2 maxextents 100);
6.manually allocating extents
sql> alter table table_name allocate extent(size 500k datafile 'c:/oracle/data.dbf');
7.move tablespace   �U�d��表空�?br /> sql> alter table employee move tablespace users;
8.deallocate of unused space deallocate的闲�|�空�?br /> sql> alter table table_name deallocate unused [keep integer]
9.truncate a table   截断�?br /> sql> truncate table table_name;
10.drop a table 删除�?br /> sql> drop table table_name [cascade constraints];
11.drop a column 删除�?br /> sql> alter table table_name drop column comments cascade constraints checkpoint 1000;
alter table table_name drop columns continue;
12.mark a column as unused
sql> alter table table_name set unused column comments cascade constraints;
alter table table_name drop unused columns checkpoint 1000;
alter table orders drop columns continue checkpoint 1000
data_dictionary : dba_unused_col_tabs

　　�W�四�?索引
1.creating function-based indexes 建立��Z��功能的烦�?br /> sql> create index summit.item_quantity on summit.item(quantity-quantity_shipped);
2.create a B-tree index    创造一个B树烦�?br /> sql> create [unique] index index_name on table_name(column,.. asc/desc) tablespace
sql> tablespace_name [pctfree integer] [initrans integer] [maxtrans integer]
sql> [logging | nologging] [nosort] storage(initial 200k next 200k pctincrease 0
sql> maxextents 50);
3.pctfree(index)=(maximum number of rows-initial number of rows)*100/maximum number of rows
4.creating reverse key indexes   创造逆�{关键指标
sql> create unique index xay_id on xay(a) reverse pctfree 30 storage(initial 200k
sql> next 200k pctincrease 0 maxextents 50) tablespace indx;
5.create bitmap index   创徏位图索引
sql> create bitmap index xay_id on xay(a) pctfree 30 storage( initial 200k next 200k
sql> pctincrease 0 maxextents 50) tablespace indx;
6.change storage parameter of index   改变存储参数指标
sql> alter index xay_id storage (next 400k maxextents 100);
7.allocating index space    分配索引�I�间
sql> alter index xay_id allocate extent(size 200k datafile 'c:/oracle/index.dbf');
8.alter index xay_id deallocate unused;    改变指数xay_id deallocate�?/p>

�W�五�?�U�束
1.define constraints as immediate or deferred     界定制约��x��或�g�?br /> sql> alter session set constraint[s] = immediate/deferred/default;
set constraint[s] constraint_name/all immediate/deferred;
2. sql> drop table table_name cascade constraints
sql> drop tablespace tablespace_name including contents cascade constraints
3. define constraints while create a table    界定限制,同时创徏一个表
sql> create table xay(id number(7) constraint xay_id primary key deferrable
sql> using index storage(initial 100k next 100k) tablespace indx);
primary key/unique/references table(column)/check
4.enable constraints    使制�U?br /> sql> alter table xay enable novalidate constraint xay_id;
5.enable constraints     使制�U?br /> sql> alter table xay enable validate constraint xay_id;

�W�六�?LOAD数据
1.loading data using direct_load insert
sql> insert /*+append */ into emp nologging
sql> select * from emp_old;
2.parallel direct-load insert
sql> alter session enable parallel dml;
sql> insert /*+parallel(emp,2) */ into emp nologging
sql> select * from emp_old;
3.using sql*loader
sql> sqlldr scott/tiger \
sql> control = ulcase6.ctl \
sql> log = ulcase6.log direct=true

�W�七�?数据整理
1.using expoty
$exp scott/tiger tables(dept,emp) file=c:\emp.dmp log=exp.log compress=n direct=y
2.using import
$imp scott/tiger tables(dept,emp) file=emp.dmp log=imp.log ignore=y
3.transporting a tablespace
sql>alter tablespace sales_ts read only;
$exp sys/.. file=xay.dmp transport_tablespace=y tablespace=sales_ts
triggers=n constraints=n
$copy datafile
$imp sys/.. file=xay.dmp transport_tablespace=y datafiles=(/disk1/sles01.dbf,/disk2
/sles02.dbf)
sql> alter tablespace sales_ts read write;
4.checking transport set
sql> DBMS_tts.transport_set_check(ts_list =>'sales_ts' ..,incl_constraints=>true);
在表transport_set_violations 中查�?br /> sql> dbms_tts.isselfcontained 为true 是，表示自包�?br /> �W�八�? 密码安全与资源管�?br /> 1.controlling account lock and password
sql> alter user juncky identified by oracle account unlock;
2.user_provided password function
sql> function_name(userid in varchar2(30),password in varchar2(30),
old_password in varchar2(30)) return boolean
3.create a profile : password setting
sql> create profile grace_5 limit failed_login_attempts 3
sql> password_lock_time unlimited password_life_time 30
sql>password_reuse_time 30 password_verify_function verify_function
sql> password_grace_time 5;
4.altering a profile
sql> alter profile default failed_login_attempts 3
sql> password_life_time 60 password_grace_time 10;
5.drop a profile
sql> drop profile grace_5 [cascade];
6.create a profile : resource limit
sql> create profile developer_prof limit sessions_per_user 2
sql> cpu_per_session 10000 idle_time 60 connect_time 480;
7. view => resource_cost : alter resource cost
dba_Users,dba_profiles
8. enable resource limits
sql> alter system set resource_limit=true;
�W�九�?用户��理
1.create a user: database authentication
sql> create user juncky identified by oracle default tablespace users
sql> temporary tablespace temp quota 10m on data password expire
sql> [account lock|unlock] [profile profilename|default];
2.change user quota on tablespace
sql> alter user juncky quota 0 on users;
3.drop a user
sql> drop user juncky [cascade];
4. monitor user
view: dba_users , dba_ts_quotas
�W�十�?�Ҏ��理
1.system privileges: view => system_privilege_map ,dba_sys_privs,session_privs
2.grant system privilege
sql> grant create session,create table to managers;
sql> grant create session to scott with admin option;
with admin option can grant or revoke privilege from any user or role;
3.sysdba and sysoper privileges:
sysoper: startup,shutdown,alter database open|mount,alter database backup controlfile,
alter tablespace begin/end backup,recover database
alter database archivelog,restricted session
sysdba: sysoper privileges with admin option,create database,recover database until
4.password file members: view:=> v$pwfile_users
5.O7_dictionary_accessibility =true restriction access to view or tables in other schema
6.revoke system privilege
sql> revoke create table from karen;
sql> revoke create session from scott;
7.grant object privilege
sql> grant execute on dbms_pipe to public;
sql> grant update(first_name,salary) on employee to karen with grant option;
8.display object privilege : view => dba_tab_privs, dba_col_privs
9.revoke object privilege
sql> revoke execute on dbms_pipe from scott [cascade constraints];
10.audit record view :=> sys.aud$
11. protecting the audit trail
sql> audit delete on sys.aud$ by access;
12.statement auditing
sql> audit user;
13.privilege auditing
sql> audit select any table by summit by access;
14.schema object auditing
sql> audit lock on summit.employee by access whenever successful;
15.view audit option : view=> all_def_audit_opts,dba_stmt_audit_opts,dba_priv_audit_opts,dba_obj_audit_opts
16.view audit result: view=> dba_audit_trail,dba_audit_exists,dba_audit_object,dba_audit_session,dba_audit_statement
�W�十一�? 规则��理�?br /> 1.create roles
sql> create role sales_clerk;
sql> create role hr_clerk identified by bonus;
sql> create role hr_manager identified externally;
2.modify role
sql> alter role sales_clerk identified by commission;
sql> alter role hr_clerk identified externally;
sql> alter role hr_manager not identified;
3.assigning roles
sql> grant sales_clerk to scott;
sql> grant hr_clerk to hr_manager;
sql> grant hr_manager to scott with admin option;
4.establish default role
sql> alter user scott default role hr_clerk,sales_clerk;
sql> alter user scott default role all;
sql> alter user scott default role all except hr_clerk;
sql> alter user scott default role none;
5.enable and disable roles
sql> set role hr_clerk;
sql> set role sales_clerk identified by commission;
sql> set role all except sales_clerk;
sql> set role none;
6.remove role from user
sql> revoke sales_clerk from scott;
sql> revoke hr_manager from public;
7.remove role
sql> drop role hr_manager;
8.display role information
view: =>dba_roles,dba_role_privs,role_role_privs,dba_sys_privs,role_sys_privs,role_tab_privs,session_roles
�W�十二章: 备䆾与恢�?br /> 1. v$sga,v$instance,v$process,v$bgprocess,v$database,v$datafile,v$sgastat
2. Rman need set dbwr_IO_slaves or backup_tape_IO_slaves and large_pool_size
3. Monitoring Parallel Rollback
> v$fast_start_servers , v$fast_start_transactions
4.perform a closed database backup (noarchivelog)
> shutdown immediate
> cp files /backup/
> startup
5.restore to a different location
> connect system/manager as sysdba
> startup mount
> alter database rename file '/disk1/../user.dbf' to '/disk2/../user.dbf';
> alter database open;
6.recover syntax
--recover a mounted database
>recover database;
>recover datafile '/disk1/data/df2.dbf';
>alter database recover database;
--recover an opened database
>recover tablespace user_data;
>recover datafile 2;
>alter database recover datafile 2;
7.how to apply redo log files automatically
>set autorecovery on
>recover automatic datafile 4;
8.complete recovery:
--method 1(mounted databae)
>copy c:\backup\user.dbf c:\oradata\user.dbf
>startup mount
>recover datafile 'c:\oradata\user.dbf;
>alter database open;
--method 2(opened database,initially opened,not system or rollback datafile)
>copy c:\backup\user.dbf c:\oradata\user.dbf (alter tablespace offline)
>recover datafile 'c:\oradata\user.dbf' or
>recover tablespace user_data;
>alter database datafile 'c:\oradata\user.dbf' online or
>alter tablespace user_data online;
--method 3(opened database,initially closed not system or rollback datafile)
>startup mount
>alter database datafile 'c:\oradata\user.dbf' offline;
>alter database open
>copy c:\backup\user.dbf d:\oradata\user.dbf
>alter database rename file 'c:\oradata\user.dbf' to 'd:\oradata\user.dbf'
>recover datafile 'e:\oradata\user.dbf' or recover tablespace user_data;
>alter tablespace user_data online;
--method 4(loss of data file with no backup and have all archive log)
>alter tablespace user_data offline immediate;
>alter database create datafile 'd:\oradata\user.dbf' as 'c:\oradata\user.dbf''
>recover tablespace user_data;
>alter tablespace user_data online
5.perform an open database backup
> alter tablespace user_data begin backup;
> copy files /backup/
> alter database datafile '/c:/../data.dbf' end backup;
> alter system switch logfile;
6.backup a control file
> alter database backup controlfile to 'control1.bkp';
> alter database backup controlfile to trace;
7.recovery (noarchivelog mode)
> shutdown abort
> cp files
> startup
8.recovery of file in backup mode
>alter database datafile 2 end backup;
9.clearing redo log file
>alter database clear unarchived logfile group 1;
>alter database clear unarchived logfile group 1 unrecoverable datafile;
10.redo log recovery
>alter database add logfile group 3 'c:\oradata\redo03.log' size 1000k;
>alter database drop logfile group 1;
>alter database open;
or >cp c:\oradata\redo02.log' c:\oradata\redo01.log
>alter database clear logfile 'c:\oradata\log01.log';

Masen 2010-08-02 17:25 发表评论

Masen — Mon, 25 Feb 2008 09:56:00 GMT
JDBC下各�U�数据库的连接字�W�串和驱动类一�?

DB2 v8:
jdbc:db2://host/dbName
COM.ibm.db2.jdbc.net.DB2Driver

DB2 v9
jdbc:db2://host/dbName:deferPrepares=false;
com.ibm.db2.jcc.DB2Driver

Informix:
jdbc:informix-sqli://host/dbName:INFORMIXSERVER=server
com.informix.jdbc.IfxDriver

SQLServer:
jdbc:sqlserver://host;DatabaseName=dbName
com.microsoft.jdbc.sqlserver.SQLServerDriver

MySQL�Q?br /> jdbc:mysql://host/dbName?useUnicode=true&characterEncoding=GBK
com.mysql.jdbc.Driver

Oracle�Q?br /> jdbc:oracle:thin:@host:dbName
oracle.jdbc.driver.OracleDriver

Sybase�Q?br /> jdbc:sybase:Tds:host/dbName
com.sybase.jdbc2.jdbc.SybDriver

Teradata:
jdbc:teradata://host/dbName
com.ncr.teradata.TeraDriver

Masen 2008-02-25 17:56 发表评论

分页sql

Masen — Sun, 20 May 2007 08:42:00 GMT

MSSQL

如在ms   sqlserver   用此语句�Q?nbsp;
select   top   2   *   from   test01   ��׃��只显�C�前2条记录，


MYSQL

select   *   from   your_table   where   ....   limit   2;

使用limit��可以了.

Oracle的语�?
select * from (select rownum r ,* from test) tt
where tt.r > 50 and tt.r <= 100; (最好用PLSQL游标来解�?

DB2中：
select * from payment fetch first 5 row only --查前5条记�?nbsp;

MySQL

select * from Cat limit ?,?
select * from Cat limit 20000,100
从Cat表中�W?0000条开始取�?00条记录，卌��录号�?0000�?0099的记�?nbsp;

select * from Cat limit ?
select * from Cat limit 100
从Cat表中取出记录号�ؓ1�?00的记�?nbsp;

select * from Cat order by rand() limit ?
select * from Cat order by rand() limit 100
从Cat表中随机取出100条记�?nbsp;

Oracle

select * from (select *, rownum rownum_ from Cat where rownum <= ?) where rownum_ > ?
select * from (select *, rownum rownum_ from Cat where rownum <= 20099) where rownum_ > 19999
从Cat表中�W?0000条开始取�?00条记录，卌��录号�?0000�?0099的记�?nbsp;

select * from Cat where rownum <= ?
select * from Cat where rownum <= 100
从Cat表中取出记录号�ؓ1�?00的记�?nbsp;

select * from (select * from Cat order by dbms_random.value) where rownum < ?
select * from (select * from Cat order by dbms_random.value) where rownum < 100
从Cat表中随机取出100条记�?nbsp;

HSQLDB

select * from Cat limit ? ?
select * from Cat limit 20000 100
从Cat表中�W?0000条开始取�?00条记录，卌��录号�?0000�?0099的记�?nbsp;

select * from Cat top ?
select * from Cat top 100
从Cat表中取出记录号�ؓ1�?00的记�?nbsp;

Masen 2007-05-20 16:42 发表评论

Mysql常用函数列表

Masen — Fri, 11 May 2007 09:38:00 GMT

Mysql常用函数列表

字符串类

CHARSET(str) //�q�回字串字符�?br>CONCAT (string2 [,... ]) //�q�接字串
INSTR (string ,substring ) //�q�回substring首次在string中出现的位置,不存在返�?
LCASE (string2 ) //转换成小�?br>LEFT (string2 ,length ) //从string2中的左边起取length个字�W?br>LENGTH (string ) //string长度
LOAD_FILE (file_name ) //从文件读取内�?br>LOCATE (substring , string [,start_position ] ) 同INSTR,但可指定开始位�|?br>LPAD (string2 ,length ,pad ) //重复用pad加在string开�?直到字串长度为length
LTRIM (string2 ) //去除前端�I�格
REPEAT (string2 ,count ) //重复count��?br>REPLACE (str ,search_str ,replace_str ) //在str中用replace_str替换search_str
RPAD (string2 ,length ,pad) //在str后用pad补充,直到长度为length
RTRIM (string2 ) //去除后端�I�格
STRCMP (string1 ,string2 ) //逐字�W�比较两字串大小,
SUBSTRING (str , position [,length ]) //从str的position开�?取length个字�W?
TRIM([[BOTH|LEADING|TRAILING] [padding] FROM]string2) //去除指定位置的指定字�W?br>UCASE (string2 ) //转换成大�?br>RIGHT(string2,length) //取string2最后length个字�W?br>SPACE(count) //生成count个空�?/div>

数学�c?/u>

ABS (number2 ) //�l�对�?br>BIN (decimal_number ) //十进制�{二进�?br>CEILING (number2 ) //向上取整
CONV(number2,from_base,to_base) //�q�制转换
FLOOR (number2 ) //向下取整
FORMAT (number,decimal_places ) //保留��数位数
HEX (DecimalNumber ) //转十六进�?br>LEAST (number , number2 [,..]) //求最��?br>MOD (numerator ,denominator ) //求余
POWER (number ,power ) //求指�?br>RAND([seed]) //随机�?br>ROUND (number [,decimals ]) //四舍五入,decimals为小��C��数]
SIGN (number2 ) //�q�回�W�号,正负�?
SQRT(number2) //开�q�x��

日期旉��c?/u>

ADDTIME (date2 ,time_interval ) //��time_interval加到date2
CONVERT_TZ (datetime2 ,fromTZ ,toTZ ) //转换时区
CURRENT_DATE ( ) //当前日期
CURRENT_TIME ( ) //当前旉��
CURRENT_TIMESTAMP ( ) //当前旉��?br>DATE (datetime ) //�q�回datetime的日期部�?br>DATE_ADD (date2 , INTERVAL d_value d_type ) //在date2中加上日期或旉��
DATE_FORMAT (datetime ,FormatCodes ) //使用formatcodes格式昄��datetime
DATE_SUB (date2 , INTERVAL d_value d_type ) //在date2上减��M��个时�?br>DATEDIFF (date1 ,date2 ) //两个日期�?br>DAY (date ) //�q�回日期的天
DAYNAME (date ) //英文星期
DAYOFWEEK (date ) //星期(1-7) ,1为星期天
DAYOFYEAR (date ) //一�q�中的第几天
EXTRACT (interval_name FROM date ) //从date中提取日期的指定部分
MAKEDATE (year ,day ) //�l�出�q�及�q�中的第几天,生成日期�?br>MAKETIME (hour ,minute ,second ) //生成旉��?br>MONTHNAME (date ) //英文月䆾�?br>NOW ( ) //当前旉��
SEC_TO_TIME (seconds ) //�U�数转成旉��
STR_TO_DATE (string ,format ) //字串转成旉��,以format格式昄��
TIMEDIFF (datetime1 ,datetime2 ) //两个旉��?br>TIME_TO_SEC (time ) //旉��转秒数]
WEEK (date_time [,start_of_week ]) //�W�几�?br>YEAR (datetime ) //�q�䆾
DAYOFMONTH(datetime) //月的�W�几�?br>HOUR(datetime) //��时
LAST_DAY(date) //date的月的最后日�?br>MICROSECOND(datetime) //微秒
MONTH(datetime) //�?br>MINUTE(datetime) //�?/div>

�?可用在INTERVAL中的�c�d��
DAY ,DAY_HOUR ,DAY_MINUTE ,DAY_SECOND ,HOUR ,HOUR_MINUTE ,HOUR_SECOND ,MINUTE ,MINUTE_SECOND,MONTH ,SECOND ,YEAR

Masen 2007-05-11 17:38 发表评论

代码如下	复制代码
INSERT IGNORE INTO `table_name` (`email`, `phone`, `user_id`) VALUES ('test9@163.com', '99999', '9999');

代码如下	复制代码
INSERT IGNORE INTO `table_1` (`name`) SELECT `name` FROM `table_2`;

代码如下	复制代码
REPLACE INTO `table_name`(`col_name`, ...) VALUES (...); REPLACE INTO `table_name` (`col_name`, ...) SELECT ...; REPLACE INTO `table_name` SET `col_name`='value',

代码如下	复制代码
REPLACE INTO `table_name` (`email`, `phone`, `user_id`) VALUES ('test569', '99999', '123');

代码如下	复制代码
if not exists (select phone from t where phone= '1') insert into t(phone, update_time) values('1', getdate()) else update t set update_time = getdate() where phone= '1'

代码如下	复制代码
INSERT INTO `table` (`a`, `b`, `c`) VALUES (1, 2, 3) ON DUPLICATE KEY UPDATE `c`=`c`+1; UPDATE `table` SET `c`=`c`+1 WHERE `a`=1;

代码如下	复制代码
UPDATE `table` SET `c`=`c`+1 WHERE `a`=1 OR `b`=2 LIMIT 1;

代码如下	复制代码
INSERT INTO `table_name1` (`title`, `first_name`, `last_name`, `email`, `phone`, `user_id`, `role_id`, `status`, `campaign_id`) SELECT '', '', '', `table_name2`.`email`, `table_name2`.`phone`, NULL, NULL, 'pending', 29 FROM `table_name2` WHERE `table_name2`.`status` = 1 ON DUPLICATE KEY UPDATE `table_name1`.`status`='pending'

代码如下	复制代码
INSERT INTO `class` SELECT * FROM `class1` ON DUPLICATE KEY UPDATE `class`.`course`=`class1`.`course`

代码如下	复制代码
select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

代码如下	复制代码
delete from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1) and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)

代码如下	复制代码
select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

代码如下	复制代码
delete from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count() > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count()>1)