使用 merge into 是为了根据匹配条件on(condition)利用table_source 的数据更新合并table_target的数据。
merge into 的内部处理是将 table_source 的每一条记录和table_target的每一条记录对比匹配，匹配到符合条件的 记录就会进行修改，匹配不到的话就会insert。如果table_source的匹配列中有重复值的话，等到第二次重复的列值匹配的时候，就会将第一次的update后的值再一次update,就是说合并后的table_target中会丢失在table_source中的记录！！！如果记录丢失的话，两表合并的意义何在？！！因此我们使用merge into要注意：源表匹配列中不能有重复值，否则无法匹配（报错！ ）。
查询一下ORA-30926错误的具体说明：
Oracle Error : ORA-30926
unable to get a stable set of rows in the source tables
Cause
A stable set of rows could not be got because of large dml activity or a non-deterministic where clause.
Action
Remove any non-deterministic where clauses and reissue the dml.
If there is either a many-to-one or many-to-many relationship between the source and target tables. This is not as serious as it sounds because you would normally have to MERGE a one-to-one or one-to-zero relationship as your join condition would be protected by the target's primary key.
When performing a merge statement, the table to be merged had multiplerecords with the same key used for matching. While this is ok forrecords to be inserted into the target table, Oracle doesn't like thison the update portion of the statement. The solution is to remove the duplicate or pick a matching key that is truely unique.
There is a restriction that multiple updates to the same row in the destination table is not allowed. ORA-30926 error will be returned if this is attempted.
通过上面的信息可以得知，对目标表中的相同行数据进行多次更新是不允许的，这样会导致ORA-30926错误。
追溯代码，确保MERGE INTO中USING表对于ON中的关联条件是唯一的，注意到表DW.FACT_DEAL_AUCTION_D的数据是细化到AUCTION_ID的，会存在多条相同的CUSTID和CATID维度数据。通过使用group by修改代码即可解决。
