Do we require constraints in Datawarehousing?

Question

I can understand if we can create the surrogate keys for the dimension tables. Do we require foreign key constraints for the Fact tables. If we dont use the foreign keys what would be the effect during the ETL load. Im maintaining an exception table where all the failure records will be inserted. In that case what is the use of foreign constraint to create, even disable and enable also not required.
Pls post your thoughts !!
Kishan

Answer 1

Hi Borkur. Sorry for the confusion...
This is an association I automatically do.
You are right, constraints and indexes are different structures, but they are highly connected to each other. Sometimes, having a constraint, necessarily means having an index associated with it.
Take a look at this example:
create table cargos_t
(cd_cgo number primary key,
nm_cgo varchar2(30) not null)
create table cidades_t
(cd_cid number primary key,
nm_cid varchar2(100) not null,
UF varchar2(2) not null)
create table emp_t
(cd_emp number primary key,
nm_emp varchar2(30),
cd_dep references depto_t,
sal number (10,2) not null,
com number (2,2),
dt_adm date not null,
dt_dms date,
cod_cgo number references cargos_t,
cod_cid number references cidades_t)
Note that I never created manually any indexes.
And then, query dictionary views, you'll see there's some indexes for those tables.
SQL> select A.INDEX_NAME, 
  2         A.TABLE_NAME,
  3         A.TABLE_TYPE,
  4         B.CONSTRAINT_NAME,
  5         B.CONSTRAINT_TYPE
  6  from user_indexes A,  USER_CONSTRAINTS B
  7  where A.table_name in ('EMP_T', 'CARGOS_T', 'CIDADES_T')
  8    AND A.TABLE_NAME = B.TABLE_NAME
  9    and b.index_name = b.constraint_name;
INDEX_NAME                     TABLE_NAME                     TABLE_TYPE  CONSTRAINT_NAME                C
SYS_C0034289                   CARGOS_T                       TABLE       SYS_C0034289                   P
SYS_C0034292                   CIDADES_T                      TABLE       SYS_C0034292                   P
SYS_C0034295                   EMP_T                          TABLE       SYS_C0034295                   PWhen you create a Primary Key constraint, Oracle creates an Index for it automatically.
Plus:
create table cargos_t
(cd_cgo number primary key,
  nm_cgo varchar2(30) not null)
  1  select A.INDEX_NAME,
  2         A.TABLE_NAME,
  3         A.TABLE_TYPE,
  4         B.CONSTRAINT_NAME,
  5         B.CONSTRAINT_TYPE
  6  from user_indexes A,  USER_CONSTRAINTS B
  7  where A.table_name in ('CARGOS_T')
  8    AND A.TABLE_NAME = B.TABLE_NAME
  9*   and b.index_name = b.constraint_name
SQL> /
INDEX_NAME                     TABLE_NAME                     TABLE_TYPE  CONSTRAINT_NAME                C
SYS_C0034289                   CARGOS_T                       TABLE       SYS_C0034289                   P
SQL> alter table cargos_t
  2  add constraint uk_nm_cgo unique (nm_cgo);
Table altered.
SQL> select A.INDEX_NAME,
  2         A.TABLE_NAME,
  3         A.TABLE_TYPE,
  4         B.CONSTRAINT_NAME,
  5         B.CONSTRAINT_TYPE
  6  from user_indexes A,  USER_CONSTRAINTS B
  7  where A.table_name in ('CARGOS_T')
  8    AND A.TABLE_NAME = B.TABLE_NAME
  9    and b.index_name = b.constraint_name
10  /
INDEX_NAME                     TABLE_NAME                     TABLE_TYPE  CONSTRAINT_NAME                C
SYS_C0034289                   CARGOS_T                       TABLE       SYS_C0034289                   P
UK_NM_CGO                      CARGOS_T                       TABLE       SYS_C0034289                   P
SYS_C0034289                   CARGOS_T                       TABLE       UK_NM_CGO                      U
UK_NM_CGO                      CARGOS_T                       TABLE       UK_NM_CGO                      UAs you may notice, Oracle also creates indexes for Unique keys.
This is the reason why I associated constraints with indexes. But you are right when you say they are different objects in the database.
Regards,
Marcos
Message was edited by:
Marcos Spínola