My Gridview updation is not working.

I am not able to update my gridview row.

NOTES

1>My database table don't have a primary key and I will not be able to alter the table to add primary key.

#>I am updating the gridview as mentioned below

UpdateCommand = UPDATE OptumRx_Mst_Opioid_Members

SET DOB=@dob_New,

FName=@fName_New, LName=@lName_New, ZIP=@zip_new

WHERE DOB=@dob_Old AND FName=@fName_Old AND LName=@lName_Old AND ZIP=@zip_Old

2> I have kept the DataKeyName =""

4> I have used the HiddenField to store the oldValues of gridview

5> Within GridView1_RowUpdating, I am able to get the oldValues & newValues

6> I am setting updateParameter within GridView1_RowUpdating.

Please suggest what am I missing