Question

oracle嵌套查询的问题

单独执行select substr(max(FILE_NAME),-6,2) from dba_data_files where tablespace_name ='ITSCHDSERVERDATA';和select to_char('02'+1,'00') from dual;都能执行，为什么select to_char('(select substr(max(FILE_NAME),-6,2) from dba_data_files where tablespace_name ='ITSCHDSERVERDATA')'+1,'00') from dual;就不行呢

Answer 1

select to_char((select substr(max(FILE_NAME),-6,2) from dba_data_files where tablespace_name ='ITSCHDSERVERDATA')+1,'00') from dual
里面嵌套的select的外层不需要用单引号。