jdbc获取结果行数,如何获取JDBC中的行数？

I've executed a JDBC query to obtain a resultset. Before iterating over it, I'd like to quickly find out how many rows were returned. How can I do this with high performance?

I'm using Java 6, Oracle 11g, and the latest Oracle JDBC drivers.

解决方案

You're going to have to do this as a separate query, for example:

SELECT COUNT(1) FROM table_name

Some JDBC drivers might tell you but this is optional behaviour and, more to the point, the driver may not know yet. This can be due to how the query is optimised eg two example execution strategies in Oracle are to get all rows as quickly as possible or to get the first row as quickly as possible.

If you do two separate queries (one a count and the other the query) then you'll need to do them within the same transaction. This will work well on Oracle but can be problematic on other databases (eg SQL Server will either show you uncommitted data or block on an external uncommitted update depending on your isolation level whereas Oracle supports an isolation level that gives you a transactionally consistent view of the data without blocking on external updates).

Normally though it doesn't really matter how many rows there are. Typically this sort of query is either batch processed or paged and either way you have progress information in the form of rows loaded/processed and you can detect the end of the result set (obviously).

jdbc获取结果行数,如何获取JDBC中的行数？相关推荐

java异步线程数_spring异步service中处理线程数限制详解
情况简介 spring项目,controller异步调用service的方法,产生大量并发. 具体业务: 前台同时传入大量待翻译的单词,后台业务接收单词,并调用百度翻译接口翻译接收单词并将翻译结果保存 ...
Excel怎样设置标题行，Excel工作表中标题行的处理
Excel怎样设置标题行,工作表中标题行的处理 Excel做几十.几百行的表格很平常.看下部的数据时看不到表格的标题行,让人搞不清每一列的天文数字究竟代表什么意思.而且正常打印输出时,只有第一页能打印 ...
sql 如何设置行级锁_SQL Server中的行级安全性简介
sql 如何设置行级锁 In this article, I'm going to discuss Row-Level Security in SQL Server. RLS or Row-Level ...
国行switch服务器在维护中,国行Switch是否锁区锁服？你关心的问题都将在这里解答...
国行Nintendo Switch已于今日(12月10日)正式发售,我们已经拿到国行Switch,并对一些备受关注的问题进行了验证,要点如下: • 国行Switch可以玩海外版卡带,海外版游戏也可以正 ...
html拆分单元格多行,拆分一个单元格中多行字符到不同单元格
有如下格式excel数据: Number ID Assignment 1 A ...
css textarea行数_限制textarea中的行数并使用jQuery显示行数
喵喵时光机一个非常丑陋但以某种方式起作用的示例指定了textarea行然后在js中 $("textarea").on('keydown keypress keyup',fun ...
php读取文件行读,如何在php中按行读取文件
您可以使用fgets()函数逐行读取文件: $handle = fopen("inputfile.txt", "r"); if ($handle) { whil ...
mysql查询周数_MySQL：查询中从周数开始的周日期范围
我有一个数据库表,看起来像这样: | id | clock | info ---------------------------------------------- | 1 | 1262556754 ...
java中获取文件总行数_关于java：如何以有效的方式获取文件中的行数？
本问题已经有最佳答案,请猛点这里访问. 我有一个大文件. 它包括大约3.000-20.000行. 如何使用Java获取文件中的行总数? 从你的评论到答案来判断,你要找的词是"有效的" ...
如何在MyEclipse中显示行数
转载自如何在MyEclipse中显示行数如何在MyEclipse中显示行数呢?myeclipse在默认情况下不显示行数时,用户可以自己设置显示行数,行数可以帮助我们方便的查看代码. 首先,打开w ...

jdbc获取结果行数,如何获取JDBC中的行数？

jdbc获取结果行数,如何获取JDBC中的行数？相关推荐

最新文章

热门文章