ORACLE的UPDATE更新多表的方法

关于ORACLE的UPDATE更新多表的问题
有以下几种方式可以实现:
一种是：
      update table1
            set (field1,field2...) =
                    (Select Field1,field2....
                          from table2
                        where table1.field1=table2.field1)
        where table1.field1 in (select field1 from table2)

二种是：
      将table1,table2相关联字段建立主键Primary key 或Union key
      Update (Select Table1.field1,table1.field2,table2.field1,table2.field2
                          from table1,table2
                        where Table1.Field1=table2.field1)

            Set table1.table2=table2.table2,
                    table1.fieldn=table2.tablen,
                    ......
      table1的Field1和table2的field1将需要建立主键或唯一索引才行

三种是：
merge into table1
using table2
          on (table1.field1=table2.field1 and ....)
      when matched then Update set table1.field2=table2.field2,
                                                                table1.fieldn=table2.fieldn,
                                                                ......
when not matched then [doing other thing]