IF..ELSE statement in simple SQL SELECT queries

I have 2 tables tmp1 and tmp2. They looks like below:

tmp1:

+----+------+---------+---------+
| id | name | add1    | add2    |
+----+------+---------+---------+
| 1  | NULL | NULL    | NULL    |
| 2  | NULL | NULL    | NULL    |
| 3  | mum1 | rajpur1 | rajpur2 |
| 4  | mum3 | rajpur3 | rajpur4 |
+----+------+---------+---------+

tmp2:

+----+------+---------+---------+
| id | name | add1    | add2    |
+----+------+---------+---------+
| 1  | NULL | NULL    | NULL    |
| 2  | mum  | rajpur  | rajpur1 |
| 3  | NULL | NULL    | NULL    |
| 4  | mum2 | rajpur2 | rajpur3 |
+----+------+---------+---------+

I want to use if..else statement here to retrieve some data like:

Case 1: if id=1 then (select * from tmp1 where id=1)

Case 2: if id=2 then (select * from tmp2 where id=2)

Case 3: if id=3 then (select * from tmp1 where id=3)

Case 4: if id=4 then (select * from tmp1 where id=4)  

I'm trying to solve this question from last 2 days. pls help it's really important.