进行数据文件维护时，发现数据文件的名称存在大小写差异。
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在某个时间点以后创建的数据文件，名称中的db_name和“datafile”都是大写，而以前都是小写。
查询官方文档 Directory for Datafiles and Controlfiles Become Uppercase in 18.3 DBCA. (Doc ID 2542927.1)
在18.3.0.0版本开始，内部设计上的变化导致了此问题。
同时还指向一个internal的文档，无权限浏览：
BUG:29294715 - 18.3 DBCA UPPERCASING DB_UNIQUE_NAME FOR DIRECTORY OF DATA FILES AND CONTROL FILES.
进一步分析发现，我们将数据库升级到19c，并将compatible由11.2.0.4改为19.3.0.0后，数据文件路径就改为大写了。
使用文件系统作为存储介质的数据库未出现此问题。
Directory for Datafiles and Controlfiles Become Uppercase in 18.3 DBCA. (Doc ID 2542927.1)
Oracle Database Configuration Assistant - Version 18.3.0.0.0 and later
Information in this document applies to any platform.
When you specified lowercase "DB_UNIQUE_NAME" variable(for example:orcl) in DB:18.3 DBCA to create DB instance
after the instance be created, you will find the directory of data files and control files contains uppercase DB_UNIQUE_NAME which you specified.
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/u01/app/oracle/oradata/ORCL
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This result is different from the previous version(DB:12.2/DB:12.1).
If we save the DBCA scripts which can be generated by DBCA, we could see that even if you specified lowercase DB_UNIQUE_NAME in DBCA,
the script is to create uppercase DB_UNIQUE_NAME in the directory path of data files and control files.
Using DB:18.3 DBCA to create database instance and specified lowercase "DB_UNIQUE_NAME" variable.
It is a limitation according to current design.
The following method can avoid this issue.
STEP 1: Generate the DBCA Scripts.
STEP 2: Change the uppercase DB_UNIQUE_NAME to lowercase DB_UNIQUE_NAME manually.
STEP 3: Execute these scripts to create DB instance.