从结果集中选择几行mysql java

Question

i have used a select command in my java program and stored its value in the result set. now while looping in the resultset i want to use a select command which will select the first 5 lines of the resultset and insert into other table. for the second time, it should select the next 5 lines and insert into the table. and for the third time, so on..

Statement s = connection.createStatement();
s.executeQuery("Select * from table1");
ResultSet res = s.getResultSet();
while(res.next()){
 // here i want to select the first 5 lines of the result set and insert in the second       table
}

Answer 1

Statement s = connection.createStatement();
s.executeQuery("Select * from table1");
ResultSet res = s.getResultSet();

while(res.next()){
    // here i want to select the first 5 lines of the result set and insert in the second       table
    while(res.next() && (res.getRow()%5) !=0){
        //select from this table
        //call insert method(what selected)
    }
}

Answer 2

Please add a falg and use that is it

int i=0;

while(res.next() && i< 5){
//select from this table
//call insert method(what selected)
i++;
}

Answer 3

在while循环内动态创建另一个插入查询，并在while循环外执行

Answer 4

I would suggest changing your query using LIMIT and using a PreparedStatement. Something like:

SELECT * FROM table1 LIMIT ?,?

This has a couple of advantages:

• You are not fetching everything in one shot - can be sometimes a performance benefit if you've a lot many rows to deal with in your table
• You can change pre-define the number of elements that you want to fetch in every single batch

So your code will look something like this:

PreparedStatement ps = null;
ResultSet rs = null;
final int FETCH_LIMIT   = 5; //number of elements to fetch per batch
final int BATCH_LIMIT   = 3; //number of batches you would want

int currentRows = 0;
try{
    ps = connection.prepareStatement("SELECT * FROM table1 LIMIT ?,?");
    for(int currentBatch = 0; currentBatch < BATCH_LIMIT; currentBatch++){
        ps.clearParameters();
        ps.setInt(1, currentRows);
        ps.setInt(2, currentRows + FETCH_LIMIT);

        try{
            rs = ps.executeQuery();
            while(rs.next()){
                // do your work
            }
        }catch(Exception exe){
            //manage exception
        }finally{
            //manage resultset
        }
        currentRows += FETCH_LIMIT;
    }
}catch(Exception exe){
    //Handle your exception
}
finally{
    //Manage your resources
}