Mysql分页－Limit

一．Mysql 的Limit用法

在我们使用查询语句的时候，经常会返回一部分，即按页返回．

mysql已经为我们提供了这样一个功能．

SELECT * FROM table LIMIT [offset,] rows | rows OFFSET offset

LIMIT 子句可以被用于强制 SELECT 语句返回指定的记录数。LIMIT 接受一个或两个数字参数。参数必须是一个整数常量。如果给定两个参数，第一个参数指定第一个返回记录行的偏移量，第二个参数指定返回记录行的最大数目。初始记录行的偏移量是 0(而不是 1)．

mysql> SELECT * FROM table LIMIT 5,10; // 检索记录行 6-15

//为了检索从某一个偏移量到记录集的结束所有的记录行，可以指定第二个参数为 -1
// 检索记录行 96-last.
mysql> SELECT * FROM table LIMIT 95,-1;

//如果只给定一个参数，它表示返回最大的记录行数目
//换句话说，LIMIT n 等价于 LIMIT 0,n
mysql> SELECT * FROM table LIMIT 5; //检索前 5 个记录行

二．分页的思想

使用Limit用法实现分页，最关键的就是获得他的两个参数．

我们可以根据选择的页数来获得偏移量（int offset = (currPage - 1) * PageParam.pageSize ）每页所显示的记录数即为显示的最大数目．

三．分页的实现

分页类

public class PageParam {
private int currPage ; // 当前页
private int totalPage ; // 总页
private int rowCount ; // 总记录数
public static int pageSize = 2; // 页大小
private List<Article> data ; // 数据
public int getCurrPage() {return currPage;
}
public void setCurrPage(int currPage) {
this.currPage = currPage;
}
public int getTotalPage() {
return totalPage;
}
public void setTotalPage(int totalPage) {
this.totalPage = totalPage;
}
public int getRowCount() {
return rowCount;
}
public void setRowCount(int rowCount) {
//根据总记录数确定总页数
int totalPage = rowCount / pageSize;
if (rowCount % pageSize > 0) {
totalPage += 1;
}
setTotalPage(totalPage);
this.rowCount = rowCount;
}
public int getPageSize() {
return pageSize;
}
public void setPageSize(int pageSize) {
this.pageSize = pageSize;
}
public List<Article> getData() {
return data;
}
public void setData(List<Article> data) {
this.data = data;
}
}

Service层

@Service
public class Services {
@Resource
Dao1 dao;
public Configure getConfigured(){
return dao.getConfigured();
}
public void setConfigure(Configure configure){
dao.setConfigure(configure);
}
public int getRowCount() {return dao.getRowCount();}
public PageParam getArticle(PageParam pageParam) {
int currPage = pageParam.getCurrPage();
// limit offset, size
int offset = (currPage - 1) * PageParam.pageSize ;
int size = PageParam.pageSize;
Map<String, Object> params = new HashMap<String, Object>();
params.put("offset", offset);
params.put("size", size);

List<Article> articleList = dao.getArticle(params);
pageParam.setData(articleList);

return pageParam;
}

Controller层

@Controller
public class ArticleController {

@Resource
Services service;

//文章列表
@RequestMapping(value = "/article",method = RequestMethod.GET)
public String getArticle(Model map,HttpServletRequest request){
String currPageStr = request.getParameter("page");
int currPage = 1;
try {
currPage = Integer.parseInt(currPageStr);
} catch (Exception e) {
}
// 获取总记录数
int rowCount = service.getRowCount();
PageParam pageParam = new PageParam();
pageParam.setRowCount(rowCount);
if (pageParam.getTotalPage() < currPage) {
currPage = pageParam.getTotalPage();
}
pageParam.setCurrPage(currPage);
pageParam = service.getArticle(pageParam);
List<String> allcategory = service.getAllCategory();
map.addAttribute("pageParamData", pageParam.getData());
map.addAttribute("allcategory",allcategory);
request.setAttribute("pageParam", pageParam);

return "article";
}

Mapper

<mapper namespace="com.dao.Dao">
<select id="getRowCount" resultType="int">
select count(*) from article WHERE deleted = 'n'
</select>

<select id="getArticle" resultType="Article" parameterType="map">
select * from article
where deleted = 'n'
limit ${offset}, ${size}
</select>
</mapper>