oracle新手求高手帮我做两道题目

Question

题目一
表A
+---+----+-----+----+
|id | A1 |  A2 | A3 |
+---+----+-----+----+
|1  | aaa|     |    |
|2  | bbb|     |    |
|3  | ccc|     |    |
+---+----+-----+----+
表B
+---+----+-----+
|id |  A2|  A3 |
+---+----+-----+
|1  |苏州|员工1|
|2  |南京|员工2|
|4  |无锡|员工4|
+---+----+-----+更新表A 得到
+---+----+-----+-----+
|id | A1 |  A2 | A3  |
+---+----+-----+-----+
|1  | aaa| 苏州|员工1| 
|2  | bbb| 南京|员工2|
+---+----+-----+-----+=============================================================
题目二
表A
+---+----+-----+----+
|id | A1 |  A2 | A3 |
+---+----+-----+----+
|1  | aaa|     |    |
|2  | bbb|     |    |
|3  | ccc|     |    |
+---+----+-----+----+表B
+---+----+-----+
|id |  A2|  A3 |
+---+----+-----+
|1  |苏州|员工1|
|2  |南京|员工2|
|4  |无锡|员工4|
+---+----+-----+合并两张表
要得出
+---+----+-----+-----+
|id | A1 |  A2 | A3  |
+---+----+-----+-----+
|1  | aaa| 苏州|员工1| 
|2  | bbb| 南京|员工2|
|3  | ccc|     |     |
|4  |    | 无锡|员工4|
+---+----+-----+-----+

Answer 1

SQL> select a.id,a.a1,b.a2,b.a3 from a ,b where a.id = b.id;        ID A1         A2         A3
---------- ---------- ---------- ----------
         1 aaa        sz         employer1
         2 bbb        nj         employer2SQL> select a.id,a.a1,b.a2,b.a3 from a left join b on a.id = b.id
  2  union all
  3  select id,null,a2,a3 from b where id not in (select id from a);        ID A1         A2         A3
---------- ---------- ---------- ----------
         1 aaa        sz         employer1
         2 bbb        nj         employer2
         3 ccc
         4            wx         employer4SQL> 

Answer 2

1.select a.id,a.a1,b.a2,b.a3 from a join b on a.id = b.id;2.select a.id,a.a1,b.a2,b.a3 from a full join b on a.id = b.id