Best practice for Yes / No column

Question

Hello,
When the column stores only Yes / No Values. What is the right definition for that column. Is the following right pertaining IS_PAID column :
CREATE TABLE ABSENCE
    ID         NUMBER (3) NOT NULL ,
    USER_ID    NUMBER (3) NOT NULL ,
    IS_PAID    VARCHAR2 (1 BYTE) DEFAULT 'N' NOT NULL ,
ALTER TABLE ABSENCE ADD CHECK
  IS_PAID IN ('N', 'Y')
;Regards,

Answer 1

>
Yes, but I wouldn't make too much fuss about the choice between function-based indexes and virtual columns - in either case they're generally seen as an add-on that requires a change to the code to work.
>
True - but the following is an example query that includes the 'fuss' that I like to avoid by using a VIRTUAL column.
From your Oracle Scratchpad of December 16, 2010 'FBI oddities'
http://jonathanlewis.wordpress.com/2010/12/16/fbi-oddities/#more-5249 (OP's issue is pretty much the one you discuss in that article.)
select     /*+ index(t1) t1_f1 */     v1 from     t1 where     decode(state,'CLOSED', to_number(null), n1 ) = 100 ; Many developers, especially the less-experienced ones, can't write those 'decodes' properly. And they certainly aren't 'self-documening or as straightforward as a simple "WHERE column = 'value'".
For me simpler is better.
Edited by: rp0428 on Apr 23, 2013 12:34 PM to add code sample
These are the two choices when using the sample DDL below (based on your sample from the link above):
select * from t2 where decode(state,'OPEN', state, null ) = 'OPEN'       
select * from t2 where virtual_state = 'OPEN'I prefer to use, and train developers to use the second choice. It is simpler and much more intuitive.
create table t2 (
    state       varchar2(10),
    n1      number,
    v1      varchar2(10),
    padding varchar2(100),
    virtual_state varchar2(10) GENERATED ALWAYS AS (
    case when state = 'OPEN' then state else null end ) VIRTUAL
create index t2_state on t2(decode(state,'OPEN', state, null ));
create index t2_virtual_state on t2(virtual_state);
insert into t2 (state, n1, v1, padding)
    select
        decode(mod(rownum,100),0,'OPEN','CLOSED'),
        rownum,
        lpad(rownum,10,0),
        rpad('x',100,'x')
    from
        all_objects
    where
        rownum <= 5000 ;
select * from t2 where decode(state,'OPEN', state, null ) = 'OPEN';       
select * from t2 where virtual_state = 'OPEN';