SQL*Plus tips #3: Iterators and recursions

We all used to iterators, recursions and branching in programming, but sql*plus does not have such commands. Today I will show how to do iterators/recusions.

Suppose we want to call a script 3 times. So it would be convenient if we can do it like:

@iterate 3 @some_script

It is very easy: We can recursively call the script by reducing variable until it is greater than zero. and if a variable is zero, then call an empty “NULL” script.
iterate.sql:

-- initializing input parameters as i showed in previous tips:
@inc/input_params_init.sql;
-- for example max number of input parameters = 14:
def _INIT_PARAMS = '"&3" "&4" "&5" "&6" "&7" "&8" "&9" "&10" "&11" "&12" "&13" "&14" "&15" "&16"'
def _ITER = "&1"

prompt ------   iteration &_ITER start: "@&2  -----------;
set termout off


col _SCRIPT    new_val _SCRIPT   noprint;
col _CONTINUE  new_val _CONTINUE noprint;
col _PARAMS    new_val _PARAMS   noprint;
select 
   replace('"&3" "&4" "&5" "&6" "&7" "&8" "&9" "&10" "&11" "&12" "&13" "&14" "&15" "&16"'
          ,'${ITER}'
          ,'&_ITER'
          )          as "_PARAMS"
  ,case 
      when &1 > 0 then 'iterate '||(&1 - 1)
      else 'inc/null'
   end               as "_CONTINUE"
  ,case 
      when &1 > 0 then '&2' 
      else 'inc/null'
   end               as "_SCRIPT"
from dual;
set termout on

@&_script            &_PARAMS
@&_CONTINUE &_SCRIPT &_INIT_PARAMS

As you see i also added option to pass iteration_number as input parameter, so we can call it like: @iterate 3 script.sql ${ITER}
And null.sql in “inc” directory is just empty file.

Lets test it:

SQL> $cat test.sql
select &1 a,'&2' b,'&3' c from dual;

SQL> @iterate 3 test.sql 1 2 3
------   iteration 3 start: "@test.sql  -----------

         A B C
---------- - -
         1 2 3

------   iteration 2 start: "@test.sql  -----------

         A B C
---------- - -
         1 2 3

------   iteration 1 start: "@test.sql  -----------

         A B C
---------- - -
         1 2 3

------   iteration 0 start: "@test.sql  -----------

SQL> @iterate 2 test.sql 1 2 ${ITER}
------   iteration 2 start: "@test.sql  -----------

         A B C
---------- - -
         1 2 2

------   iteration 1 start: "@test.sql  -----------

         A B C
---------- - -
         1 2 1

------   iteration 0 start: "@test.sql  -----------

Note that last string “iteration 0 start” just means that it is last empty call. I made this only for showing how we can do postprocessing after all iterations.
Ok, it works good, but with a little modification we can also add option to call such script with list of values too:

See how it works:

-- iterate by list of values  (7,3,10):
SQL> @iterate (7,3,10) test.sql 1 2 ${ITER}
******   iteration 7 start: "@test.sql  ***********

         A B C
---------- - -
         1 2 7

******   iteration 3 start: "@test.sql  ***********

         A B C
---------- - -
         1 2 3

******   iteration 10 start: "@test.sql  ***********

         A B C
---------- - --
         1 2 10

-- now with simple 2 iterations:
SQL> @iterate 2 test.sql 1 2 ${ITER}
******   iteration 2 start: "@test.sql  ***********

         A B C
---------- - -
         1 2 2

******   iteration 1 start: "@test.sql  ***********

         A B C
---------- - -
         1 2 1

So if you call script with “iterate N …” it will iterate N times, and if you specify “iterate (X,Y,…,Z)” it will iterate by this list.

PS. About a branching i will wrote later…