[应用架构] Mysql分页技术

1.使用mysql进行分页比较简单，

下面我结合查询条件来加以说明。这里我使用原生态JDBC进行查询，分页查询要用到以下SQL语句：

sql = "select * from sems_fractional_record Limit "+(currentPage-1)*pageSize+", "+pageSize+" "

复制代码
Limit关键字后面接从第几个记录开始，然后逗号号隔开，后面再接显示多少条记录。

2. 查询总页码数

结合查询条件，这里会有点儿复杂，只是因为它的查询条件比较复杂，它有集中器UID还有时间日期，而且它们都是变化的，UID有两个变化，而时间日期有四个变公，结合起来2*4 =8，则共有8种查询语句，如下所示：

try{

if(mark == 1){

//后面可以加上附加条件

sql = "select count(*) from sems_fractional_record ";

}

if(mark == 2){

sql = "select count(*) from sems_fractional_record where concentUID='"+concentUID+"'";

}

if(mark == 3){

sql = "select count(*) from sems_fractional_record where datetime='"+datetime+"'";

}

if(mark == 4){

sql = "select count(*) from sems_fractional_record where concentUID='"+concentUID+"' and datetime='"+datetime+"'";

}

if(mark == 5){

sql = "select count(*) from sems_fractional_record where datetime like'%"+datetime+"%'"; //'%"+userName+"%'"

}

if(mark == 6){

sql = "select count(*) from sems_fractional_record where datetime like'%"+datetime+"%' and concentUID='"+concentUID+"'" ;

}

if(mark == 7){

sql = "select count(*) from sems_fractional_record where datetime between '"+datetime+"' and '"+endTime+"'";

}

if(mark == 8){

sql = "select count(*) from sems_fractional_record where datetime between '"+datetime+"' and '"+endTime+"'and concentUID='"+concentUID+"'" ;

}

rs = this.query(sql);

if(rs.next()){

//得到总记录数

rowCount = rs.getInt(1);

//计算总页数

pageCount = rowCount%pageSize ==0 ? rowCount/pageSize : rowCount/pageSize+1 ;

}

}catch(Exception evt){

logger.info("查询总页数出现异常");

}

3.查询每页的记录数

这里的方法是分页进行查询，是要多少数据才加载多少条数据，比如默认加载第一页的数据，则它不会加其他页中的数据，从而效率和性能比较好，加载每页记录数的代码如下所示：

try {

if(mark == 1){

//后面可以加上附加条件

sql = "select * from sems_fractional_record ";

}

if(mark == 2){

sql = "select * from sems_fractional_record where concentUID='"+concentUID+"'";

}

if(mark == 3){

sql = "select * from sems_fractional_record where datetime='"+datetime+"'";

}

if(mark == 4){

sql = "select * from sems_fractional_record where concentUID='"+concentUID+"' and datetime='"+datetime+"'";

}

if(mark == 5){

sql = "select * from sems_fractional_record where datetime like'%"+datetime+"%'"; //'%"+userName+"%'"

}

if(mark == 6){

sql = "select * from sems_fractional_record where datetime like'%"+datetime+"%' and concentUID='"+concentUID+"'" ;

}

if(mark == 7){

sql = "select * from sems_fractional_record where datetime between '"+datetime+"' and '"+endTime+"'";

}

if(mark == 8){

sql = "select * from sems_fractional_record where datetime between '"+datetime+"' and '"+endTime+"'and concentUID='"+concentUID+"'" ;

}

//加上后面的分页条件,后缀suffix

String sqlSuffix = " Limit "+(currentPage-1)*pageSize+", "+pageSize+" ";//"select uid from sems_fractional_record";

//组成复合查询

sql=sql+ sqlSuffix;

rs = this.query(sql);

注意： 在使用原生态JDBC的时候，一定要将数据库连接对象关闭或即时放入连接池中，不然会影响服务器性能。甚至于内存溢出等问题。

4.最后再举一例mysql联合（union）查询的例子，SQL代码如下：

1.

------------------------

-----电表复杂报表

select w.uid,w.theyear year,max(january)january,max(february)february,max(march)march,max(april)april,max(may)may,max(june)june,max(july)july,max(august)august,

max(september)september,max(october)october,max(november)november,max(december)december

from(

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,IF(SUBSTR(t.datetime,6,2)='01',t.curMonthCoulometer,0)january,0 february,0 march,0 april,0 may,0 june,0 july,

0 august,0 september, 0 october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,IF(SUBSTR(t.datetime,6,2)='02',t.curMonthCoulometer,0)february,0 march,0 april,0 may,0 june,0 july,

0 august,0 september, 0 october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,IF(SUBSTR(t.datetime,6,2)='03',t.curMonthCoulometer,0) march,0 april,0 may,0 june,0 july,

0 august,0 september, 0 october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february ,0 march ,IF(SUBSTR(t.datetime,6,2)='04',t.curMonthCoulometer,0) april,0 may,0 june,0 july,

0 august,0 september, 0 october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,IF(SUBSTR(t.datetime,6,2)='05',t.curMonthCoulometer,0) may,0 june,0 july,

0 august,0 september, 0 october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,IF(SUBSTR(t.datetime,6,2)='06',t.curMonthCoulometer,0) june,0 july,

0 august,0 september, 0 october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,IF(SUBSTR(t.datetime,6,2)='07',t.curMonthCoulometer,0) july,

0 august,0 september, 0 october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,

IF(SUBSTR(t.datetime,6,2)='08',t.curMonthCoulometer,0) august,0 september, 0 october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,

0 august,IF(SUBSTR(t.datetime,6,2)='09',t.curMonthCoulometer,0) september, 0 october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,

0 august,0 september, IF(SUBSTR(t.datetime,6,2)='10',t.curMonthCoulometer,0) october,0 november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,

0 august,0 september, 0 october,IF(SUBSTR(t.datetime,6,2)='11',t.curMonthCoulometer,0) november,0 december from qo_1_nfschina.sems_ammeter_history_data t

UNION

SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,

0 august,0 september, 0 october,0 november,IF(SUBSTR(t.datetime,6,2)='12',t.curMonthCoulometer,0) december from qo_1_nfschina.sems_ammeter_history_data t

)w

group by w.uid,w.theyear

2.JAVA代码程式.

try {

String sql = "select w.uid,w.theyear year,max(january)january,max(february)february,max(march)march,max(april)april," +

"max(may)may,max(june)june,max(july)july,max(august)august, max(september)september,max(october)october," +

"max(november)november,max(december)december from(" +

"SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,IF(SUBSTR(t.datetime,6,2)='01',t.curMonthCoulometer,0)january," +

"0 february,0 march,0 april,0 may,0 june,0 july,0 august,0 september, 0 october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' " +

" UNION SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,IF(SUBSTR(t.datetime,6,2)='02',t.curMonthCoulometer,0)february,0 march,0 april,0 may," +

"0 june,0 july,0 august,0 september, 0 october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' UNION " +

"SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,IF(SUBSTR(t.datetime,6,2)='03',t.curMonthCoulometer,0) march,0 april,0 may,0 june,0 july,0" +

" august,0 september, 0 october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' UNION " +

"SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february ,0 march ,IF(SUBSTR(t.datetime,6,2)='04',t.curMonthCoulometer,0) april,0 may,0 june,0 july,0" +

" august,0 september, 0 october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' " +

" UNION SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,IF(SUBSTR(t.datetime,6,2)='05',t.curMonthCoulometer,0) may,0 june,0 " +

"july,0 august,0 september, 0 october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' " +

"UNION SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,IF(SUBSTR(t.datetime,6,2)='06',t.curMonthCoulometer,0) june,0 july,0" +

" august,0 september, 0 october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' " +

"UNION SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,IF(SUBSTR(t.datetime,6,2)='07',t.curMonthCoulometer,0) july,0" +

" august,0 september, 0 october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' " +

"UNION SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,IF(SUBSTR(t.datetime,6,2)='08'," +

"t.curMonthCoulometer,0) august,0 september, 0 october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' " +

"UNION SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,0 august,IF(SUBSTR(t.datetime,6,2)='09'," +

"t.curMonthCoulometer,0) september, 0 october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' " +

" UNION SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,0 august,0 september, IF(SUBSTR(t.datetime,6,2)='10'," +

"t.curMonthCoulometer,0) october,0 november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' " +

"UNION SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,0 august,0 september, 0 october," +

"IF(SUBSTR(t.datetime,6,2)='11',t.curMonthCoulometer,0) november,0 december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"' " +

" UNION SELECT t.uid,SUBSTR(t.datetime,1,4)theyear,0 january,0 february,0 march,0 april,0 may,0 june,0 july,0 august,0 september, 0 october,0 november," +

"IF(SUBSTR(t.datetime,6,2)='12',t.curMonthCoulometer,0) december from sems_ammeter_history_data t where uid='"+ammeterUID.trim()+"' and concent_uid='"+concenUID.trim()+"')" +

"w" +

" group by w.uid,w.theyear ";

//执行查询

rs = query(sql);

它用到的两个表(sems_ammeter_real_data 和sems_ammeter_history_data ):

----创建实时电表数据

DROP TABLE IF EXISTS `sems_ammeter_real_data`;

CREATE TABLE `sems_ammeter_real_data` (

`Id` bigint(20) NOT NULL auto_increment,

`uid` varchar(255) default NULL,

`type` int(255) default NULL,

`phaseA` varchar(255) default NULL,

`voltageA` double(20,2) default NULL,

`electricityA` double(20,2) default NULL,

`powerA` double(20,2) default NULL,

`powerFactorA` double(20,2) default NULL,

`phaseB` varchar(255) default NULL,

`voltageB` double(20,2) default NULL,

`electricityB` double(20,2) default NULL,

`powerB` double(20,2) default NULL,

`powerFactorB` double(20,2) default NULL,

`phaseC` varchar(255) default NULL,

`voltageC` double(20,2) default NULL,

`electricityC` double(20,2) default NULL,

`powerC` double(20,2) default NULL,

`powerFactorC` double(20,2) default NULL,

`coulometer` double(20,3) default NULL,

`datetime` varchar(255) default NULL,

`concent_uid` varchar(12) default NULL,

PRIMARY KEY (`Id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

------创建历史电表数据表格

DROP TABLE IF EXISTS `sems_ammeter_history_data`;

CREATE TABLE `sems_ammeter_history_data` (

`Id` bigint(20) NOT NULL auto_increment,

`uid` varchar(255) default NULL,

`totalCoulometer` double(20,3) default NULL,

`curMonthCoulometer` double(20,3) default NULL,

`datetime` varchar(255) default NULL,

`concent_uid` varchar(12) default NULL,

PRIMARY KEY (`Id`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

这部分代码比较复杂，有想了解的可以私下一起讨论之，共同进步.

(完....待续)