Some important SQL about Oracle

    --view system time
    select sysdate from dual;
    --view charset
    select userenv('language') from dual;

    select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;

    select 1+2 from dual;

    create sequence aaa increment by 1 start with 1;

    select aaa.nextval from dual;  
    select aaa.currval from dual;

   --view table dll
    SELECT DBMS_METADATA.GET_DDL('TABLE',u.table_name) FROM USER_TABLES u where u.TABLE_NAME='AAATEST';

    --view all table include a Column
    select table_name  from user_TAB_COLUMNS where COLUMN_NAME='DESCRIPTION';
  
    -- select * from USER_TABLES
   
    --oracle query all table and Index include some column
    select *  from user_TAB_COLUMNS where COLUMN_NAME='DESCRIPTION'
   
    --oracle query all table include some column
    select col.table_name from user_TAB_COLUMNS col,USER_TABLES  tab where col.COLUMN_NAME='DESCRIPTION'   and col.table_name=tab.table_name