Question

这不应该是一个非常简单的操作吗？但是，我发现既没有size()也没有length()方法。

Answer 1

改为执行SELECT COUNT(*) FROM ...查询。

OR

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

在任何一种情况下，您都不必遍历整个数据。

Answer 2

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
}

Answer 3

好吧，如果您的ResultSet类型为ResultSet.TYPE_FORWARD_ONLY，您希望保持这种方式（并且不>切换为ResultSet.TYPE_SCROLL_INSENSITIVE或{{ 1}}以便能够使用ResultSet.TYPE_SCROLL_INSENSITIVE）。

我建议一个非常好用且高效的黑客，你在顶部添加第一个包含行数的虚假/虚假行。

实施例

假设您的查询如下

.last()

，您的输出看起来像

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

只需将代码重构为以下内容：

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]

您的查询输出现在将类似于

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);

所以你必须

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]

Answer 4

int i = 0;
while(rs.next()) {
    i++;
}

Answer 5

使用rs.last()

时出现异常

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

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

默认情况下它是ResultSet.TYPE_FORWARD_ONLY，这意味着您只能使用rs.next()

解决方案是：

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

Answer 6

这是一种简单的行计数方法。

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

Answer 7

获取ResultSet大小的方法，不需要使用ArrayList等

int size =0;  
if (rs != null)   
{  
rs.beforeFirst();  
 rs.last();  
size = rs.getRow();
}

现在您将获得大小，如果您想要打印ResultSet，在打印之前也使用以下代码行，

rs.beforeFirst();

Answer 8

[速度考虑]

这里的很多人建议使用ResultSet.last()，但为此你需要打开连接作为ResultSet.TYPE_SCROLL_INSENSITIVE，对于Derby嵌入式数据库来说，最多10次 SLOWER 而不是{{ 1}}。

根据我对嵌入式Derby和H2数据库的微测试，在SELECT之前调用ResultSet.TYPE_FORWARD_ONLY要快得多。

Here is in more detail my code and my benchmarks

Answer 9

我检查了 ResultSet 界面的运行时值，发现它几乎都是 ResultSetImpl 。 ResultSetImpl有一个名为getUpdateCount()的方法，它返回您要查找的值。

此代码示例应该足够了：
ResultSet resultSet = executeQuery(sqlQuery);
double rowCount = ((ResultSetImpl)resultSet).getUpdateCount()

我意识到向下转换通常是一种不安全的程序，但这种方法还没有让我失望。

Answer 10

        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);

     }

Answer 11

今天，我用这个逻辑为什么我不知道得到RS的数量。

int chkSize = 0;
if (rs.next()) {
    do {  ..... blah blah
        enter code here for each rs.
        chkSize++;
    } while (rs.next());
} else {
    enter code here for rs size = 0 
}
// good luck to u.

Answer 12

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();

Answer 13

我遇到了同样的问题。在执行解决后以这种方式使用ResultSet.first()：

if(rs.first()){
    // Do your job
} else {
    // No rows take some actions
}

文档（link）：

boolean first()
    throws SQLException
将光标移动到此ResultSet对象的第一行。

退货：

true如果光标处于有效状态   行; false如果结果集中没有行

投掷：

SQLException - 如果发生数据库访问错误;在闭合的结果集上调用此方法，或者结果集类型为TYPE_FORWARD_ONLY

SQLFeatureNotSupportedException - 如果JDBC驱动程序不支持   这个方法

<强>时间：

1.2

Answer 14

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

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

Answer 15

为列命名..

String query = "SELECT COUNT(*) as count FROM

将ResultSet对象中的列引用到int并从那里执行逻辑..

PreparedStatement statement = connection.prepareStatement(query);
statement.setString(1, item.getProductId());
ResultSet resultSet = statement.executeQuery();
while (resultSet.next()) {
    int count = resultSet.getInt("count");
    if (count >= 1) {
        System.out.println("Product ID already exists.");
    } else {
        System.out.println("New Product ID.");
    }
}

如何获得java.sql.ResultSet的大小？

15 个答案: