oracle-DDL备份原始定义

[unknowissue]

Oracle 的logmnr方法对DDL SQL_UNDO为空。
1、再做DDL之前，保存对象的定义，比如alter table时，备份的是create table 的定义，能知道之前是什么类型。
2、存储过程的替换也可以保留上一份的定义，回滚比较方便
3、回滚操作还是得DBA来搞。

[codecov]

Codecov Report

Merging #1332 (d77a9fc) into master (fea32d2) will decrease coverage by 0.04%.
The diff coverage is 46.42%.

@@            Coverage Diff             @@
##           master    #1332      +/-   ##
==========================================
- Coverage   75.66%   75.62%   -0.05%     
==========================================
  Files          81       81              
  Lines       12507    12535      +28     
==========================================
+ Hits         9463     9479      +16     
- Misses       3044     3056      +12     

Impacted Files	Coverage Δ
sql/engines/oracle.py	50.56% <46.42%> (+0.36%)	⬆️

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