table A
|id|attr1|
----------
|1 | A   |
|2 | B   |
|3 | C   |
|5 | D   |
----------


table B
|id|attr2|
----------
|2 | X   |
|3 | Y   |
|4 | Z   |
----------

how can i get table C from table A and B 

table C
|id|attr1|attr2|
----------------
|1 | A   |Null |
|2 | B   |X    |
|3 | C   |Y    |
|5 | D   |Null |
----------------