如何在Java中两次使用同一结果集

Question

I would like to use same result set twice, once is to check whether it is empty and execute code based on the result, and then, using (resultset.next() the second result set will always skip a line because of the first result set

Here's my code so far :

connection = DriverManager.getConnection(connection);
statement = (Statement) connection.createStatement();
resultset = statement.executeQuery(query);

String id = "0";
String idfromdb;

if(resultset.next() == false){
  System.out.println("table is empty")
  statement.executeUpdate(" INSERT INTO table VALUES ('value') ");
}

else{
  while(resultset.next()){
    idfromdb = resultset.getString("value")
    if(! idfromdb = id){
      System.out.println("no similar data has been found");
    }    
    else{
      System.out.println("similar data has been found");
    }
  }
}

Answer 1

When you call resultset.next() it will fetch one record,so you need to call previous() to reset the cursor

The full code:

boolean hasRecord = true;
if(!resultset.next()){// you are missing ) here
    System.out.println("table is empty")
    statement.executeUpdate(" INSERT INTO table VALUES ('value') ");
    hasRecord = false;
}
if(hasRecord){
   resultset.previous();//move to the previous record
}

Answer 2

Change to do-while loop:

if(resultset.next() == false{
    System.out.println("table is empty")
    statement.executeUpdate(" INSERT INTO table VALUES ('value') ");
} else {
  do  {
    idfromdb = resultset.getString("value")
    if(! idfromdb = id){
        System.out.println("no similar data has been found");
    }

    else{
        System.out.println("similar data has been found");
    }
  } while(resultset.next());
}

do-while evaluates its expression at the bottom of the loop instead of the top.