Set autoincrement value for each value in row -- php

[eluser]masentinel900[/eluser]
Hello guys!!

Really I'm a bit confused about how can I set this requirement.

I need to set a row in my table like serial type, But I need to set before some requirements. such as that for each value in the row start the serial counter.

[For example]

ROW-1 -- ROW-2
1 1
1 2
1 3
1 4
1 5
1 6
2 1
2 2
1 7
1 8
2 3
2 4


This example means that for each value in the ROW-1 start a counter from 1 until infinite.
Really now I don't know how can I get it.
Please if do you have an idea, or maybe you has made this before. let me know.