JDBC PreparedStatement execute执行后成功插入数据库 确返回false 为什么？

public boolean add(StudentAddAction stu){

String sql = " INSERT INTO student(name,sex,birthday,address,emailNum,telephone,departmentId,majorId,gybh) " +
" values(?,?,?,?,?,?,?,?,?)";

boolean b = false;
PreparedStatement stmt = null;
try {
stmt = con.prepareStatement(sql);
stmt.setString(1, stu.getName());
stmt.setString(2, stu.getSex());
stmt.setString(3, stu.getBirthday());
stmt.setString(4, stu.getAddress());
stmt.setString(5, stu.getEmailNum());
stmt.setString(6, stu.getTelephone());
stmt.setString(7, stu.getDepartmentId());
stmt.setString(8, stu.getMajorId());
stmt.setString(9, stu.getGybh());
b = stmt.execute();
if(b){
System.out.println("操作成功!"+b);
}else {
System.out.println(b);
}
} catch (SQLException e) {
e.printStackTrace();
if(stmt!=null){
try {
stmt.close();//关闭statement对象链接
} catch (SQLException e1) {
e1.printStackTrace();
}
}
}
return b;
}