RMAN中%d %t %s %u，%p，%c 等代替变量的意义

backup incremental level 0 database format='LEV0_%d_%t_%U_%s＿%p' 
format=string 文件路径和名称的格式串，其中可包含宏变量：
%c copy ID
%p backup piece ID
%s backup set ID
%e log sequence
%h log thread ID
%d database name
%n database name(x填充到8个字符)
%I DBID
%f file ID
%F DBID, day, month, year, and sequencer的复合
%N tablespace name
%t timestamp
%M mh mm格式
%Y year yyyy格式
%u backup set+time((x填充到8个字符)
%U %u_%p_%c
%% %
The format specifier %U is replaced with unique filenames for the files when you take backups.