How to do a loop in Oracle SQL Oracle Database Tips by Donald BurlesonAugust 24,  2015

Question:  I have a need to do a loop in my SQL without using PL/SQL.  I understand that PL/SQL was create for process logic like IF and LOOPING, but can Oracle SQL support loop constructs directly?  I want to use Oracle SQL to perform a FOR loop.

Answer:  SQL was first developed as a "Structured query Language", although you could argue that SQL is not structured, for only for queries, and not a language since SQL is normally embedded into a host language like C or PL/SQL.  However, SQL is expending, and Oracle SQL now indirectly supports many of the functions of a procedural language such as branching (see the CASE operator) and rudimentary loop constructs.

In this example below, we see Oracle SQL with a FOR loop, embedded into the xmltable stored procedure.  This SQL also materializes a intermediate result set by using the SQL WITH clause:

SQL> with t as
(
  select date '2008-06-01' d1, date '2008-06-10' d2 from dual
)
select d1 + i days
  from t, xmltable('for $i in 0 to xs:int(D) return $i' passing xmlelement(d, d2-d1)
                                                        columns i integer path '.')

So, while Oracle SQL does not directly support while loops of for loops, there is extended syntax for looping within some stored procedures that are embedded into Oracle SQL.

Reader comments:

I always enjoy your site. I saw someone request a loop in SQL so I tried your SQL loop code.  I decided to make my own version of SQL looping (which is a lot longer than yours, but of course, I can understand it! :)

Set Term &OnOff

Column RunProg1 New_Value Run_Code_Or_End
column RunProg2 New_Value Run_Loop_Or_Stop

Select         Case When Counter <= (Select Length(Ename)
                                       From Emp
                                      Where Rownum <2)
                    Then 'Code'
                    Else 'EndLoop'
                 End
               As
       RunProg1,
       --------------------------------------------------
               Case When Counter <= (Select Length(Ename)
                                       From Emp
                                      Where Rownum <2)
                    Then 'Looper'
                    Else ' '
                 End
               As
       RunProg2
  From GTT_CountHolder ;

Set Term On

@&Run_Code_Or_End

@&Run_Loop_Or_Stop

Code is the actual code that we want to run multiple times. It runs the query and then updates the Counter in the temp table.

code.sql

Column Character Format A9

Select Ename ,
       -------------------------------
       -- Show position
       -------------------------------
                (Select Counter
                  from GTT_CountHolder )
                As
       Position,
       --------------------------------
       -- Show character
       -- Substr(field,position,length)
       --------------------------------
                Substr(Ename                       /* Field    */ 
                      , (Select Counter
                           from GTT_CountHolder )  /* Position */ 
                      ,1)                          /* Length   */
                As
       Character        
       -------------------------------
  From Emp
 Where Rownum < 2;

Update GTT_CountHolder
   Set Counter = Counter + 1;

EndLoop.SQL

Truncate Table GTT_CountHolder ; Drop Table GTT_CountHolder ;

Lynn Tobias

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