Mysql delete 5th element of a table

Question

I have a table:

 ID Friend
John    Rita
John    Jack
Jack    Rita
Rita    John
John    Peter
John    Owen
John    Eric
John    Louis

I want to write a query where I delete all ID 's after the 5th element. In other words I want to keep for each ID maximum 5 friends .

I have tried with a group by or something like that, but I don't now exactly how I have to do the delete.

The result must be:

  ID    Friend
John    Rita
John    Jack
Jack    Rita
Rita    John
John    Peter
John    Owen
John    Eric

Answer 1

Short answer, no. The reason is that RDBMS's do not do not guarantee the order of entries .

If you need to be certain of the rows you are deleting, then you will need to know the order. I would recommend starting by adding an auto incrementing primary key column. From that, you will at least be certain of the order of entries. Eg:

ALTER TABLE table_name ADD column_name INT AUTO_INCREMENT PRIMARY KEY;

Note: This will only guarantee the order of future entries, not previously inserted entries.