Using CASE in a SQL predicate to return variable IN values ...

Question

Environment:
Oracle EE 10.2.0.2 on AIX 5.3
I am trying to use a CASE statement in a SQL predicate to fill in the values needed in an 'IN' clause.
Here is my test case:
create table tt (model varchar2(10), brand varchar2(10));
insert into tt (model, brand) values ('modela','ajax');
insert into tt (model, brand) values ('modelb','ajax');
insert into tt (model, brand) values ('modelc','acme');
insert into tt (model, brand) values ('modeld','acme');
insert into tt (model, brand) values ('modele','acme');
insert into tt (model, brand) values ('modelf','zeus');
insert into tt (model, brand) values ('modelg','zeus');
insert into tt (model, brand) values ('modelh','mojo');
insert into tt (model, brand) values ('modeli','mojo');
insert into tt (model, brand) values ('modelj','mama');
Here is what I'm attempting to do. For a given starting letter for a brand I would like all the models printed out whose brand starts with the entered letter.
Here is what I started with:
select model, (case '&brandfirstletter'
when 'a' then '(''ajax'',''acme'')'
when 'z' then '(''zeus'')'
when 'm' then '(''mojo'')'
end) pred
from tt
where brand in
(case '&brandfirstletter'
when 'a' then '(''ajax'',''acme'')'
when 'z' then '(''zeus'')'
when 'm' then '(''mojo'')'
end);
When executed I get 'no rows selected'
I wanted to print out the results of my CASE statement just to be sure it was doing what I thought I wanted.
When I comment out the WHERE clause to see what the PRED values are I get:
gww@dwt1> /
Enter value for brandfirstletter: a
old 1: select model, (case '&brandfirstletter'
new 1: select model, (case 'a'
Enter value for brandfirstletter: a
old 8: -- (case '&brandfirstletter'
new 8: -- (case 'a'
MODEL PRED
modela ('ajax','acme')
modelb ('ajax','acme')
modelc ('ajax','acme')
modeld ('ajax','acme')
modele ('ajax','acme')
modelf ('ajax','acme')
modelg ('ajax','acme')
modelh ('ajax','acme')
modeli ('ajax','acme')
modelj ('ajax','acme')
I believe this is what I want the results of the CASE statement to look like when I select 'a' for the substitute variable but I don't get the output I would like from the table.
What am I missing?
Thanks very much!!
-gary

Answer 1

gwicke wrote:
select model, (case '&brandfirstletter'
when 'a' then '(''ajax'',''acme'')'
when 'z' then '(''zeus'')'
when 'm' then '(''mojo'')'
end) pred
from tt
where brand in
(case '&brandfirstletter'
when 'a' then '(''ajax'',''acme'')'
when 'z' then '(''zeus'')'
when 'm' then '(''mojo'')'
end);You can't do this.
ok, let's imagine you provide an 'a' as your substitution variable. What you get as a result is...
select model, (case 'a'
when 'a' then '(''ajax'',''acme'')'
when 'z' then '(''zeus'')'
when 'm' then '(''mojo'')'
end) pred
from tt
where brand in
(case 'a'
when 'a' then '(''ajax'',''acme'')'
when 'z' then '(''zeus'')'
when 'm' then '(''mojo'')'
end);
so if we logically remove the case statement as oracle would do when processing...
select model, ('(''ajax'',''acme'')') pred
from tt
where brand in ('(''ajax'',''acme'')');
Are you really going to have a brand that is stored as
(''ajax'',''acme'')as a single value?
You can't dynamically assign values to an IN list.