how can i insert data into table if the data does not exist

enter code herehow can i insert data into table if the data does not exist but if the date does exist record should not be inserted using sqlite statement any help will be appreciated.

{ }`String var=jTextField1.getText(); String var1=(String)jComboBox4.getSelectedItem(); String var2=jLabel12.getText(); try{

        String sql="INSERT INTO '"+var2+"' (ID,subject,ca,exams,total,grade,position,name,class,sex,avgageinclass,house,term,numofstudent,totalattendance,totalavg,year) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)";
        pst= conn.prepareStatement(sql);
        pst.setString(1, SN1.getText());
        pst.setString(2, SUB1.getText());
        pst.setString(3, TXT1.getText());
        pst.setString(4, TXTE1.getText());
        pst.setString(5, TT1.getText());
        pst.setString(6, GR1.getText());
        pst.setString(7, PT1.getText());
        pst.setString(8, jTextField1.getText());
        pst.setString(9, jLabel12.getText());
        pst.setString(10, jComboBox2.getSelectedItem().toString());
        pst.setString(11, jTextField2.getText());
        pst.setString(12, jComboBox3.getSelectedItem().toString());
        pst.setString(13, jComboBox4.getSelectedItem().toString());
        pst.setString(14, jTextField3.getText());
        pst.setString(15, jTextField4.getText());
        pst.setString(16, jLabel11.getText());
        pst.setString(17, jComboBox5.getSelectedItem().toString());


        pst.execute();

        }catch(Exception e){
            JOptionPane.showMessageDialog(null, e);

        }


   try{

        String sql="INSERT INTO '"+var+"' (ID,subject,ca,exams,total,grade,position,name,class,sex,avgageinclass,house,term,numofstudent,totalattendance,totalavg,year) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)";
        pst= conn.prepareStatement(sql);
        pst.setString(1, SN1.getText());
        pst.setString(2, SUB1.getText());
        pst.setString(3, TXT1.getText());
        pst.setString(4, TXTE1.getText());
        pst.setString(5, TT1.getText());
        pst.setString(6, GR1.getText());
        pst.setString(7, PT1.getText());
        pst.setString(8, jTextField1.getText());
        pst.setString(9, jLabel12.getText());
        pst.setString(10, jComboBox2.getSelectedItem().toString());
        pst.setString(11, jTextField2.getText());
        pst.setString(12, jComboBox3.getSelectedItem().toString());
        pst.setString(13, jComboBox4.getSelectedItem().toString());
        pst.setString(14, jTextField3.getText());
        pst.setString(15, jTextField4.getText());
        pst.setString(16, jLabel11.getText());
        pst.setString(17, jComboBox5.getSelectedItem().toString());


        pst.execute();

        }catch(Exception e){
            JOptionPane.showMessageDialog(null, e);

        }
        try{

           String sql="INSERT INTO '"+var+"' (ID,subject,ca,exams,total,grade,position,name,class,sex,avgageinclass,house,term,numofstudent,totalattendance,totalavg,year) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?) ";
        pst= conn.prepareStatement(sql);
        pst.setString(1, SN2.getText());
        pst.setString(2, SUB2.getText());
        pst.setString(3, TXT2.getText());
        pst.setString(4, TXTE2.getText());
        pst.setString(5, TT2.getText());
        pst.setString(6, GR2.getText());
        pst.setString(7, PT2.getText());
        pst.setString(8, jTextField1.getText());
        pst.setString(9, jLabel12.getText());
        pst.setString(10, jComboBox2.getSelectedItem().toString());
        pst.setString(11, jTextField2.getText());
        pst.setString(12, jComboBox3.getSelectedItem().toString());
        pst.setString(13, jComboBox4.getSelectedItem().toString());
        pst.setString(14, jTextField3.getText());
        pst.setString(15, jTextField4.getText());
        pst.setString(16, jLabel11.getText());
        pst.setString(17, jComboBox5.getSelectedItem().toString());
            pst.execute();

        }catch(Exception e){
            JOptionPane.showMessageDialog(null, e);

        }
        try{
            String sql="INSERT INTO '"+var+"' (ID,subject,ca,exams,total,grade,position,name,class,sex,avgageinclass,house,term,numofstudent,totalattendance,totalavg,year) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?,?) ";
        pst= conn.prepareStatement(sql);
        pst.setString(1, SN3.getText());
        pst.setString(2, SUB3.getText());
        pst.setString(3, TXT3.getText());
        pst.setString(4, TXTE3.getText());
        pst.setString(5, TT3.getText());
        pst.setString(6, GR3.getText());
        pst.setString(7, PT3.getText());
        pst.setString(8, jTextField1.getText());
        pst.setString(9, jLabel12.getText());
        pst.setString(10, jComboBox2.getSelectedItem().toString());
        pst.setString(11, jTextField2.getText());
        pst.setString(12, jComboBox3.getSelectedItem().toString());
        pst.setString(13, jComboBox4.getSelectedItem().toString());
        pst.setString(14, jTextField3.getText());
        pst.setString(15, jTextField4.getText());
        pst.setString(16, jLabel11.getText());
        pst.setString(17, jComboBox5.getSelectedItem().toString());
            pst.execute();

        }catch(Exception e){
            JOptionPane.showMessageDialog(null, e);

        }`</body>