pros and cons (now: KEEP INDEX) 2004-04-01 - By Jacques Kilchoer
> -- --Original Message-- --
> Connor McDonald
>
> Has anyone come up with a reason why you 'd want the concept
> of a KEEP INDEX option?
I can always think of a hypothetical.
e.g.
I have a table with a PK. I want to load data in the table, and the data may violate the PK (nulls in PK columns). I disable the constraint but keep the index; I then use "enable constraint exceptions into ... " to find the rows that violate the constraint and process those rows. Finally I enable the constraint again and don 't have to rebuild the index.
proof of concept
SQL > create table t (id number, name varchar2 (10),
2 constraint t_pk primary key (id)) ;
Table créée.
SQL > insert into t (id, name) values (1, 'ONE ') ;
1 ligne créée.
SQL > insert into t (id, name) values (2, 'TWO ') ;
1 ligne créée.
SQL > commit ;
Validation effectuée.
SQL > alter table t disable constraint t_pk keep index ;
Table modifiée.
SQL > insert into t (id, name) values (3, 'THREE ') ;
1 ligne créée.
SQL > ---- inserting row that violates constraint
SQL > insert into t (id, name) values (null, 'FOUR ') ;
1 ligne créée.
SQL > commit ;
Validation effectuée.
SQL > -- -- find rows that violate constraint
SQL > alter table t enable constraint t_pk exceptions into my_exceptions ;
alter table t enable constraint t_pk exceptions into my_exceptions
*
ERREUR ? la ligne 1 :
ORA-02437 (See ORA-02437.ora-code.com): cannot validate (JRK.T_PK) - primary key violated
SQL > -- -- process rows that violate constraint
SQL > delete from t where rowid in (select row_id from my_exceptions) ;
1 ligne supprimée.
SQL > commit ;
Validation effectuée.
SQL > alter table t enable constraint t_pk exceptions into my_exceptions ;
Table modifiée.
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