如何获得 java.sql.ResultSet 的大小？
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How do I get the size of a java.sql.ResultSet?
提问by Jake
Shouldn't this be a pretty straightforward operation? However, I see there's neither a size()nor length()method.
这不应该是一个非常简单的操作吗？但是，我看到既没有size()也没有length()方法。
采纳答案by finnw
Do a SELECT COUNT(*) FROM ...query instead.
SELECT COUNT(*) FROM ...改为进行查询。
OR
或者
int size =0;
if (rs != null)
{
rs.last(); // moves cursor to the last row
size = rs.getRow(); // get row id
}
In either of the case, you won't have to loop over the entire data.
在任何一种情况下，您都不必遍历整个数据。
回答by JeeBee
ResultSet rs = ps.executeQuery();
int rowcount = 0;
if (rs.last()) {
rowcount = rs.getRow();
rs.beforeFirst(); // not rs.first() because the rs.next() below will move on, missing the first element
}
while (rs.next()) {
// do your standard per row stuff
}
回答by CounterSpell
It is a simple way to do rows-count.
这是一种进行行计数的简单方法。
ResultSet rs = job.getSearchedResult(stmt);
int rsCount = 0;
//but notice that you'll only get correct ResultSet size after end of the while loop
while(rs.next())
{
//do your other per row stuff
rsCount = rsCount + 1;
}//end while
回答by Dan
I got an exception when using rs.last()
使用时出现异常 rs.last()
if(rs.last()){
rowCount = rs.getRow();
rs.beforeFirst();
}
:
：
java.sql.SQLException: Invalid operation for forward only resultset
it's due to by default it is ResultSet.TYPE_FORWARD_ONLY, which means you can only use rs.next()
这是由于默认情况下它是ResultSet.TYPE_FORWARD_ONLY，这意味着您只能使用rs.next()
the solution is:
解决办法是：
stmt=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
回答by Ben
theStatement=theConnection.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
ResultSet theResult=theStatement.executeQuery(query);
//Get the size of the data returned
theResult.last();
int size = theResult.getRow() * theResult.getMetaData().getColumnCount();
theResult.beforeFirst();
回答by Unai Vivi
Well, if you have a ResultSetof type ResultSet.TYPE_FORWARD_ONLYyou want to keep it that way (and notto switch to a ResultSet.TYPE_SCROLL_INSENSITIVEor ResultSet.TYPE_SCROLL_INSENSITIVEin order to be able to use .last()).
好吧，如果您有 aResultSet类型，ResultSet.TYPE_FORWARD_ONLY您希望保持这种方式（而不是切换到 aResultSet.TYPE_SCROLL_INSENSITIVE或ResultSet.TYPE_SCROLL_INSENSITIVE为了能够使用.last()）。
I suggest a very nice and efficient hack, where you add a first bogus/phony row at the top containing the number of rows.
我建议一个非常好的和有效的 hack，你在顶部添加一个包含行数的第一个假/假行。
Example
例子
Let's say your query is the following
假设您的查询如下
select MYBOOL,MYINT,MYCHAR,MYSMALLINT,MYVARCHAR
from MYTABLE
where ...blahblah...
and your output looks like
你的输出看起来像
true 65537 "Hey" -32768 "The quick brown fox"
false 123456 "Sup" 300 "The lazy dog"
false -123123 "Yo" 0 "Go ahead and jump"
false 3 "EVH" 456 "Might as well jump"
...
[1000 total rows]
Simply refactor your code to something like this:
只需将您的代码重构为如下所示：
Statement s=myConnection.createStatement(ResultSet.TYPE_FORWARD_ONLY,
ResultSet.CONCUR_READ_ONLY);
String from_where="FROM myTable WHERE ...blahblah... ";
//h4x
ResultSet rs=s.executeQuery("select count(*)as RECORDCOUNT,"
+ "cast(null as boolean)as MYBOOL,"
+ "cast(null as int)as MYINT,"
+ "cast(null as char(1))as MYCHAR,"
+ "cast(null as smallint)as MYSMALLINT,"
+ "cast(null as varchar(1))as MYVARCHAR "
+from_where
+"UNION ALL "//the "ALL" part prevents internal re-sorting to prevent duplicates (and we do not want that)
+"select cast(null as int)as RECORDCOUNT,"
+ "MYBOOL,MYINT,MYCHAR,MYSMALLINT,MYVARCHAR "
+from_where);
Your query output will now be something like
您的查询输出现在将类似于
1000 null null null null null
null true 65537 "Hey" -32768 "The quick brown fox"
null false 123456 "Sup" 300 "The lazy dog"
null false -123123 "Yo" 0 "Go ahead and jump"
null false 3 "EVH" 456 "Might as well jump"
...
[1001 total rows]
So you just have to
所以你只需要
if(rs.next())
System.out.println("Recordcount: "+rs.getInt("RECORDCOUNT"));//hack: first record contains the record count
while(rs.next())
//do your stuff
回答by clausavram
I checked the runtime value of the ResultSetinterface and found out it was pretty much a ResultSetImplall the time. ResultSetImpl has a method called getUpdateCount()which returns the value you are looking for.
我检查了ResultSet接口的运行时值，发现它几乎一直是一个ResultSetImpl。ResultSetImpl 有一个被调用的方法getUpdateCount()，它返回您要查找的值。
This code sample should suffice:ResultSet resultSet = executeQuery(sqlQuery);double rowCount = ((ResultSetImpl)resultSet).getUpdateCount()
此代码示例应该足够了：ResultSet resultSet = executeQuery(sqlQuery);double rowCount = ((ResultSetImpl)resultSet).getUpdateCount()
I realize that downcasting is generally an unsafe procedure but this method hasn't yet failed me.
我意识到向下转型通常是一个不安全的过程，但这种方法还没有让我失望。
回答by Peter.Chu
String sql = "select count(*) from message";
ps = cn.prepareStatement(sql);
rs = ps.executeQuery();
int rowCount = 0;
while(rs.next()) {
rowCount = Integer.parseInt(rs.getString("count(*)"));
System.out.println(Integer.parseInt(rs.getString("count(*)")));
}
System.out.println("Count : " + rowCount);
回答by bhaskar
int i = 0;
while(rs.next()) {
i++;
}
回答by Anptk
The way of getting size of ResultSet, No need of using ArrayList etc
ResultSet大小的获取方式，无需使用ArrayList等
int size =0;
if (rs != null)
{
rs.beforeFirst();
rs.last();
size = rs.getRow();
}
Now You will get size, And if you want print the ResultSet, before printing use following line of code too,
现在你会得到大小，如果你想打印结果集，在打印之前也使用以下代码行，
rs.beforeFirst();
