我如何得到一个java.sql.ResultSet的大小?

这不是一个很简单的手术吗?但是，我看到既没有size()也没有length()方法。

当前回答

如果你有一个ResultSet类型的ResultSet。TYPE_FORWARD_ONLY您希望保持这种方式(而不是切换到ResultSet)。TYPE_SCROLL_INSENSITIVE或ResultSet。TYPE_SCROLL_INSENSITIVE，以便能够使用.last())。

我建议一种非常有效的破解方法，即在顶部添加第一个包含行数的伪/伪行。

例子

假设您的查询如下

select MYBOOL,MYINT,MYCHAR,MYSMALLINT,MYVARCHAR
from MYTABLE
where ...blahblah...

输出是这样的

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]

简单地重构你的代码，就像这样:

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);

您的查询输出将如下所示

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]

所以你必须

if(rs.next())
    System.out.println("Recordcount: "+rs.getInt("RECORDCOUNT"));//hack: first record contains the record count
while(rs.next())
    //do your stuff

2013-04-10 07:46:11

其他回答

最简单的方法，运行Count(*)查询，执行resultSet.next()指向第一行，然后执行resultSet.getString(1)获得计数。代码:

ResultSet rs = statement.executeQuery("Select Count(*) from your_db");
if(rs.next()) {
   int count = rs.getString(1).toInt()
}

2019-09-30 06:37:04

当使用rs.last()时，我得到了一个异常

if(rs.last()){
    rowCount = rs.getRow(); 
    rs.beforeFirst();
}

java.sql.SQLException: Invalid operation for forward only resultset

因为默认情况下它是ResultSet。TYPE_FORWARD_ONLY，这意味着只能使用rs.next()

解决方案是:

stmt=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
    ResultSet.CONCUR_READ_ONLY);

2012-11-28 05:47:55

SELECT COUNT(*) FROM…查询。

int size =0;
if (rs != null) 
{
  rs.last();    // moves cursor to the last row
  size = rs.getRow(); // get row id 
}

在这两种情况下，都不需要遍历整个数据。

2008-10-10 16:17:36

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
}

2008-10-10 16:16:24