Using named constants in SQL rather than magic numbers

Question

We are running Oracle 7.3.4. In our system we have a number of
tables that just store static data. For example, we have a table
that stores the different types of statuses that a docket can
have:
Docket_Status: docket_status_id NUMBER(8), description VARCHAR
(100)
It has a small number of records as follows:
docket_status_id description
1 New
2 Issued
3 Completed
4 Finalised
and so on.
When we want to select all of the dockets with a status of
"New", we could do something like:
select d.*
from docket d
where d.docket_status_id = 1
However, this SQL statement is not particularly readable or
maintainable since the "1" is meaningless unless you have
memorised the id fields for the docket.
So we defined constants for each of the static data tables, in a
package of their own:
PACKAGE DOCKET_STATUS_PL IS
New_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE := 1;
Issued_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE := 2;
Completed_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE := 3;
and so on.
Ideally you could directly reference these values in SQL as
follows:
select d.*
from docket d
where d.docket_status_id = Docket_Status_Pl.New_Id
But SQL does not let allow this - an invalid column error is
raised when this is parsed.
So the package must then be changed to have functions pass back
each of the constants.
PACKAGE DOCKET_STATUS_PL IS
FUNCTION New_Id RETURN NUMBER;
PRAGMA RESTRICT_REFERENCES(New_Id, WNDS, WNPS);
FUNCTION Issued_Id RETURN NUMBER;
PRAGMA RESTRICT_REFERENCES(Issued_Id, WNDS, WNPS);
FUNCTION Completed_Id RETURN NUMBER;
PRAGMA RESTRICT_REFERENCES(Completed_Id, WNDS, WNPS);
and so on.
PACKAGE BODY DOCKET_STATUS_PL IS
N_New_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE := 1;
N_Issued_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE := 2;
N_Completed_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE := 3;
FUNCTION New_Id RETURN NUMBER IS
BEGIN
RETURN N_New_Id;
END;
FUNCTION Issued_Id RETURN NUMBER IS
BEGIN
RETURN N_Issued_Id;
END;
and so on.
Once these functions have been defined in the packages, they can
be called in a SQL statement as follows:
select d.*
from docket d
where d.docket_status_id = Docket_Status_Pl.New_Id
This makes the SQL statement a lot more readable, but has the
unfortunate by-product of having the Docket_Status_Pl.New_Id
function called for every row in the docket table. Although it
is very quick to call, once there are thousands of records in
the docket table this can add up to a lot of extra
time/processing.
An alternative is to select the constant from the dual table as
follows:
select d.*
from docket d
where d.docket_status_id = (select Docket_Status_Pl.New_Id from
dual)
This works but is not really an ideal solution, since it
decreases the readability of the SQL statement.
Does anyone know of alternatives to this approach? Ideally
package constants could be referenced from SQL, but this does
not work under our version of Oracle. Do any later versions
support this ability?
Any suggestions would be much appreciated.
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Answer 1

I don't understand why you cannot just select on the description
column if you don't no the id. If speed is a problem create a
unique not null index on the column description. Technically
this should have been done since your id column is a is not
the "REAL" primary key.
Having said that you could also create a view on top of this
table which mimics your package.
CREATE OR REPLACE VIEW name_of_view AS
SELECT DECODE(docket_status_id, 1, 'New_id',
2, 'Issued_Id',
3, 'Completed_Id',
'OTHER') alt_description,
docket_status_id description
FROM name_of_table
then select * from name_of_view
where alt_description = 'New_id'
Geoff Hardy (guest) wrote:
: We are running Oracle 7.3.4. In our system we have a number of
: tables that just store static data. For example, we have a
table
: that stores the different types of statuses that a docket can
: have:
: Docket_Status: docket_status_id NUMBER(8), description VARCHAR
: (100)
: It has a small number of records as follows:
: docket_status_id description
: 1 New
: 2 Issued
: 3 Completed
: 4 Finalised
: and so on.
: When we want to select all of the dockets with a status of
: "New", we could do something like:
: select d.*
: from docket d
: where d.docket_status_id = 1
: However, this SQL statement is not particularly readable or
: maintainable since the "1" is meaningless unless you have
: memorised the id fields for the docket.
: So we defined constants for each of the static data tables, in
a
: package of their own:
: PACKAGE DOCKET_STATUS_PL IS
: New_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE := 1;
: Issued_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE := 2;
: Completed_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE := 3;
: and so on.
: Ideally you could directly reference these values in SQL as
: follows:
: select d.*
: from docket d
: where d.docket_status_id = Docket_Status_Pl.New_Id
: But SQL does not let allow this - an invalid column error is
: raised when this is parsed.
: So the package must then be changed to have functions pass back
: each of the constants.
: PACKAGE DOCKET_STATUS_PL IS
: FUNCTION New_Id RETURN NUMBER;
: PRAGMA RESTRICT_REFERENCES(New_Id, WNDS, WNPS);
: FUNCTION Issued_Id RETURN NUMBER;
: PRAGMA RESTRICT_REFERENCES(Issued_Id, WNDS, WNPS);
: FUNCTION Completed_Id RETURN NUMBER;
: PRAGMA RESTRICT_REFERENCES(Completed_Id, WNDS, WNPS);
: and so on.
: PACKAGE BODY DOCKET_STATUS_PL IS
: N_New_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE :=
1;
: N_Issued_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE :=
2;
: N_Completed_Id CONSTANT Docket_Status.Docket_Status_Id%TYPE :=
3;
: FUNCTION New_Id RETURN NUMBER IS
: BEGIN
: RETURN N_New_Id;
: END;
: FUNCTION Issued_Id RETURN NUMBER IS
: BEGIN
: RETURN N_Issued_Id;
: END;
: and so on.
: Once these functions have been defined in the packages, they
can
: be called in a SQL statement as follows:
: select d.*
: from docket d
: where d.docket_status_id = Docket_Status_Pl.New_Id
: This makes the SQL statement a lot more readable, but has the
: unfortunate by-product of having the Docket_Status_Pl.New_Id
: function called for every row in the docket table. Although it
: is very quick to call, once there are thousands of records in
: the docket table this can add up to a lot of extra
: time/processing.
: An alternative is to select the constant from the dual table as
: follows:
: select d.*
: from docket d
: where d.docket_status_id = (select Docket_Status_Pl.New_Id
from
: dual)
: This works but is not really an ideal solution, since it
: decreases the readability of the SQL statement.
: Does anyone know of alternatives to this approach? Ideally
: package constants could be referenced from SQL, but this does
: not work under our version of Oracle. Do any later versions
: support this ability?
: Any suggestions would be much appreciated.
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