删除前检查

Question

I check Condition before delete Relationship with another table,now can check only table but more 1 table Don't check. in Database have mem_id is REFERENCES KEY in register and activity

public function check_data()
{
    $checkdata=true; 
    $query = $this->db->query("select * from register where mem_id='".$_POST['id']."'")->result();
    if(count($query)>=1)
    {
        $data['0']="register";
    }
    else
    {
        $checkdata=false;
    }

    if($checkdata==false)
    {
        $data=0;
    }

    $checkdata=true; 
    $query = $this->db->query("select * from activity where mem_id='".$_POST['id']."'")->result();
    if(count($query)>=1)
    {
        $data['1']="activity";  
    }
    else
    {
        $checkdata=false;
    }

    if($checkdata==false)
    {
        $data=0;
    }
    echo json_encode($data); 
}

index

<script>
    $(document).ready(function()
    {
        $('.delete_data').click(function()
        {
            var id = $(this).attr("id");
            if(confirm("กรุณายืนยันการลบอีกครั้ง"))
            {

                $.ajax({
                    url:'<?php echo site_url('member/check_data')?>',
                    method:"POST",
                    data:{"id":id},
                    success:function(data){
                    var data=jQuery.parseJSON(data);
                        if(data==0){
                            window.location="<?php echo site_url('member/delete/')?>"+id;
                            alert("ลบเรียบร้อย");
                        }
                        else
                        {
                            alert("ไม่สามารถลบข้อมูลได้ เนื่องจากข้อมูลมีความสัมพันธ์กับตาราง  " + data);
                        }
                    } 
                })
            }
            else
            {
                return false;
            }
        });
    });
</script>

But it can't to check for 2 table