oracle 函数

1、截取字符串：substr（date,start,length）;
SQL> select substr(to_char(sysdate,'yyyy-mm-dd hh24:mi:ss'),0,10) from dual;

SUBSTR(TO_CHAR(SYSDA
--------------------
2013-03-25

2、oracle中case语句 

-- Create table
create table HKB_TEST3
(
  USER_ID     NUMBER(4),
  AGE         NUMBER(4),
  USER_NUMBER NUMBER(4)
)

SQL> select * from hkb_test3;
 
USER_ID   AGE USER_NUMBER
------- ----- -----------
      1    12
      2    14
      3    16
      4    11
例子：

update hkb_test3
   set user_number = (select b.user_number
                        from (select a.user_id,
                                     case
                                       when a.age = 12 then
                                        '6'
                                       when a.age = 14 then
                                        '7'
                                       when a.age = 16 then
                                        '8'
                                       else
                                        '9'
                                     end user_number
                                from hkb_test3 a) b
                       where b.user_id = hkb_test3.user_id);

SQL> commit;
 
Commit complete

SQL> select * from hkb_test3;
 
USER_ID   AGE USER_NUMBER
------- ----- -----------
      1    12           6
      2    14           7
      3    16           9
      4    11           9