Question

I’m trying to do this query (in oracle) but I have some problems:

SELECT CASE 
         WHEN deptno = '10' THEN scott.seq.nextval 
                                  || 'next10' 
         WHEN deptno = '20' THEN scott.seqnextval 
                                  || 'next20' 
         WHEN deptno = '30' THEN scott.seq.currval 
                                  || 'curr' 
       END col_1 
FROM   scott.emp; 

I’m getting this results:

COL_1
----------------------------------------------
191next20
192curr
193curr
194next20
195curr
196curr
197next10
198next20
199next10
200curr
201next20
202curr
203next20
204next10
205next20
206next10
207next10

And this is what I think they should be:

COL_1
----------------------------------------------
191next20
192curr
193curr
194next20
194curr
194curr
197next10
198next20
199next10
199curr
201next20
201curr
203next20
204next10
205next20
206next10
207next10

So, why i get the next value of the sequence also when I should have the current value and not only when the case selects the next value?
Yeah, this could be done with a plsql script but I can’t.

Thanks you!

Answer 1

Interesting. Per the Oracle docs:

The statements in a WHEN clause can modify the database and call
non-deterministic functions. There is no fall-through mechanism as in
the C switch statement

Notice it doesn’t say the statements in the “true” WHEN clause. So even if the when statement is false, the nextval will fire:

select
case when 1=0 then 'next ' || seq_id.nextval
     when 1=1 then 'curr ' || seq_id.currval
end col1
from dual;

I must admit this is different than I expected.

EDIT:
See answer from ShannonSeverance