if then elsif与select case when

case when

View Code

1  select (case userid

2     when 'CUS0000003017804' then

3       '张三'

4     when 'CUS0000003017805' then

5       '李四'

6     else

7       '王五'

8   end) userid from users a where loginname = 'xxx';

View Code

 1 select case

 2          when userid ='CUS0000003017804' then

 3           '张三'

 4          when userid ='CUS0000003017805' then

 5           '李四'

 6          else

 7           '王五'

 8        end userid

 9   from users a

10  where loginname = 'xxx';

 

//字段中有符合delete等关键字的字段查询出来，不包含的不显示

select (case

         when (instr(sql_text, 'delete') > 0 or

              instr(sql_text, 'update') > 0 or

              instr(sql_text, 'insert') > 0) and

              instr(sql_text, 't_recordsql') > 0 then

          sql_text

         else

          ''

       end),length(sql_text)

  from v$sql a

 where a.LAST_ACTIVE_TIME >=

       to_date('2013/06/04 16:04:05', 'yyyy/mm/dd hh24:mi:ss')

   and a.LAST_ACTIVE_TIME <=

       to_date('2013/06/04 18:04:05', 'yyyy/mm/dd hh24:mi:ss')

 order by length(sql_text) asc

View Code

 

 

if then elsif

View Code

 1 declare

 2   v_sal users.userid%type;

 3   i     integer;

 4 begin

 5   select userid into v_sal from users where loginname = 'zhuqiaoping';

 6   if v_sal = 'zhuqiaoping' then

 7     dbms_output.put_line('张三');

 8   elsif v_sal = 'zhu' then

 9     dbms_output.put_line('李四');

10   else

11     dbms_output.put_line('王五');

12   end if;

13 

14 end;

我到现在发现的区别是，case when不能作为单独的语句块