在Java程序中使用Resultset [英] Using Resultset in Java Program

问题描述

Resultset rs=stmt.executeQuery("select count(*) from feedsca group by score order by score");

使用上面的Java代码，我从名为feedsCA的表中检索行数.

Using the above java code above, am retrieving the counts of rows from the table named feedsCA.

当尝试使用rs.getInt(1)，rs.getInt(2)，rs.getInt(3)检索计数时，我的错误如下所示，

While trying to retrieving the counts using rs.getInt(1),rs.getInt(2),rs.getInt(3), I end with an error saying as below,

Exception in thread "main" com.microsoft.sqlserver.jdbc.SQLServerException: The result set has no current row.
    at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDriverError(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerResultSet.verifyResultSetHasCurrentRow(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerResultSet.getterGetColumn(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerResultSet.getInt(Unknown Source)
    at SimpleMail.main(SimpleMail.java:151)

更新:

上述异常已解决.

但是我得到以下异常，我不知道原因.请告知.

But I get the following exception, for which I dont know the reason. Please advise.

Exception in thread "main" com.microsoft.sqlserver.jdbc.SQLServerException: The index 2 is out of range.
    at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDriverError(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerResultSet.verifyValidColumnIndex(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerResultSet.getterGetColumn(Unknown Source)
    at com.microsoft.sqlserver.jdbc.SQLServerResultSet.getInt(Unknown Source)
    at SimpleMail.main(SimpleMail.java:152)

这是我更新程序的方式.为我找到一种合理的方式，因为我能很好地理解下面的循环无法按要求工作.

This is how I have updated my program. Find me a logical way as I can understand well that the loop below will not work as required.

rs=stmt.executeQuery("select count(*) from feedsca group by score order by score");
while(rs.next()){
pw.printf(rowFormat, rs.getLong(1),"0",rs.getLong(2),rs.getLong(3));}

推荐答案

您必须将结果集的光标移动到行-通过resultSet.first()或resultSet.next().最初，光标指向第一行之前，因此是您的例外.

You have to move the cursor of the result set to a row - either by resultSet.first() or by resultSet.next(). Initially the cursor is pointing before the first row, hence your exception.

要迭代ResultSet时:

while(rs.next()) {
    ...
}

更新:对于第二个问题-(如卡萨布兰卡所指出的)，您的查询似乎只返回一列，而您要求的是第二列和第三列-均未找到.请注意，rs.getX(idx) idx中的是列，而不是行.

Update: For your second problem - (as noted by Casablanca) your query seems to return only one column, and you are asking for a 2nd and 3rd - and they are not found. Note that in rs.getX(idx) idx is the column, not the row.

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