Hi , Modic ,
Your understanding is absolutely right . There are no relationship between column c in T1 and column d in T2 ,
can be any sequence . But that's the user requirement :-)

The output can be

'a', 'b', 'c1', 'd1'
'a', 'b', 'c2', 'd2'
'a', 'b', 'c3', NULL

or

'a', 'b', 'c1', 'd2'
'a', 'b', 'c2', 'd1'
'a', 'b', 'c3', NULL

both are correct .

I feel it's not possible in SQL :-)

Please help .