PL/SQL: How to delete records in a specific manner, for example if records of specific type X exist, delete all but one record - plsql

Question

I'm trying to create a PL/SQL procedure where by I delete records that are grouped and selected by cursor but I only want one record remaining. I want to delete first by Xcomment, if there are multiple entries with id_number, activity_code, start_dt, activity_participation_code exist, then delete all but ONE entry with blank/null xcomment. If there are multiple entries with blank xcomment, then delete all but one with blank table_nmb. If multiple entries with blank table_nmb then delete highest sequence until only one is left. Essentially, I only want one record per all these fields. I'm having trouble thinking of how to do this so any help would be appreciated.
Here is my code so far:
Create Or Replace Function Y_Cleanup_Cursor
Return Sys_Refcursor
As
My_Cursor Sys_Refcursor;
Begin
Open My_Cursor For
Select Q.Id_Number, Q.Activity_Code, Q.Start_Dt, Q.Activity_Participation_Code, Q.Rec_Count, A.Xcomment, A.Table_Nmb, A.Xsequence
From (Select Id_Number, Activity_Code, Start_Dt, Activity_Participation_Code, Count(0) As Rec_Count
From Activity A
Group By Id_Number, Activity_Code, Start_Dt, Activity_Participation_Code
Having Count(0) > 1) Q,
Activity A
Where
Q.Id_Number = A.Id_Number And
Q.Activity_Code = A.Activity_Code And
Q.Start_Dt = A.Start_Dt And
Q.Activity_Participation_Code = A.Activity_Participation_Code;
Return My_Cursor;
End Y_Cleanup_Cursor;
Create Or Replace Procedure Help_Me_Please(Code In Varchar2)
Is
-- Declare Variables
-- I Stands For Internal Variable
L_Cursor Sys_Refcursor;
I_Id_Number Varchar2(10 Byte);
I_Xsequence Number (6);
I_Activity_Code Varchar2(05 Byte);
I_Start_Dt Varchar2(08 Byte);
I_Activity_Participation_Code Varchar2(02 Byte);
I_Table_Nmb Varchar2(15 Byte);
I_Xcomment Varchar2(255 Byte);
I_Rec_Count Number (6);
L_Counter Integer;
Begin
L_Cursor := Y_Cleanup_Cursor;
Loop
Fetch L_Cursor Into
I_Id_Number, I_Activity_Code, I_Start_Dt, I_Activity_Participation_Code, I_Rec_Count, I_Xcomment, I_Table_Nmb, I_Xsequence;
Select Count (Id_Number)
Into L_Counter
From Activity Where
Id_Number = I_Id_Number
And Activity_Code = I_Activity_Code
And Start_Dt = I_Start_Dt
And Activity_Participation_Code = I_Activity_Participation_Code
And Trim(Xcomment) Is Null;
If L_Counter <> I_Rec_Count Then
Begin
Delete From Activity
Where
Id_Number = I_Id_Number
And Activity_Code = I_Activity_Code
And Start_Dt = I_Start_Dt
And Activity_Participation_Code = I_Activity_Participation_Code
And Trim(Xcomment) Is Null;
end;
End If;
Exit When L_Cursor%Notfound;
End Loop;
Close L_Cursor;
End Help_Me_Please;

Answer 1

From what I gather you want to delete all rows except 1 where there are repeating columns
first make sure to backup your table:
create table [backup_table] as select * from [table];
Try This:
DELETE FROM backup_table
WHERE rowid not in
(SELECT MIN(rowid)
FROM backup_table
GROUP BY [col1], [col2]);
Col1 and col2, etc are the columns that should be identical