SQL*Plus tips. #2

I think you know the famous print_table procedure by Tom Kyte. It is really great, but a little hard(it requires create procedure or place it in anonymous block) and in last oracle versions we can do same with one simple query with xmltable/xmlsequence:

SQL> select *
  2  from
  3     xmltable( '/ROWSET/ROW/*'
  4               passing xmltype(cursor(select * from hr.employees where rownum<3))
  5               columns
  6                  col varchar2(100) path 'name()'
  7                 ,val varchar2(100) path '.'
  8        );

COL                            VAL
------------------------------ ------------------------------------------------------
EMPLOYEE_ID                    198
FIRST_NAME                     Donald
LAST_NAME                      OConnell
EMAIL                          DOCONNEL
PHONE_NUMBER                   650.507.9833
HIRE_DATE                      21-JUN-07
JOB_ID                         SH_CLERK
SALARY                         2600
MANAGER_ID                     124
DEPARTMENT_ID                  50
EMPLOYEE_ID                    199
FIRST_NAME                     Douglas
LAST_NAME                      Grant
EMAIL                          DGRANT
PHONE_NUMBER                   650.507.9844
HIRE_DATE                      13-JAN-08
JOB_ID                         SH_CLERK
SALARY                         2600
MANAGER_ID                     124
DEPARTMENT_ID                  50

20 rows selected.

It is very easy, but for conveniency we need to add “rownum”:

SQL> select *
  2  from
  3     xmltable( 'for $a at $i in /ROWSET/ROW
  4                   ,$r in $a/*
  5                     return element ROW{
  6                                       element ROW_NUM{$i}
  7                                      ,element COL_NAME{$r/name()}
  8                                      ,element COL_VALUE{$r/text()}
  9                                      }'
 10               passing xmltype(cursor(select * from hr.employees where rownum<3))
 11               columns
 12                  row_num   int
 13                 ,col_name  varchar2(30)
 14                 ,col_value varchar2(100)
 15        );

   ROW_NUM COL_NAME                       COL_VALUE
---------- ------------------------------ ------------------------------------------
         1 EMPLOYEE_ID                    198
         1 FIRST_NAME                     Donald
         1 LAST_NAME                      OConnell
         1 EMAIL                          DOCONNEL
         1 PHONE_NUMBER                   650.507.9833
         1 HIRE_DATE                      21-JUN-07
         1 JOB_ID                         SH_CLERK
         1 SALARY                         2600
         1 MANAGER_ID                     124
         1 DEPARTMENT_ID                  50
         2 EMPLOYEE_ID                    199
         2 FIRST_NAME                     Douglas
         2 LAST_NAME                      Grant
         2 EMAIL                          DGRANT
         2 PHONE_NUMBER                   650.507.9844
         2 HIRE_DATE                      13-JAN-08
         2 JOB_ID                         SH_CLERK
         2 SALARY                         2600
         2 MANAGER_ID                     124
         2 DEPARTMENT_ID                  50

20 rows selected.

Now we can create simple script for it with formatting:

Usage example:
As you see script works fine, but it is require to pass query as parameter, though sometimes it is not so convenient. For example if we want started query and later decided to show it with print_table. In that case we can create scripts with tricks from previous part:

Example:
PS. if you will use xmltype(cursor(…)) on versions less that 11.2.0.3 you can get errors with xml rewriting. In this case you need to disable it:

alter session set events '19027 trace name context forever, level 0x1';

---

Update:
Vladimir Przyjalkowski rightly pointed out that such approach will be suboptimal in case of big amount of data:

A nice toy, but i’m sure it will not tolerate big data.

It is absolutely true, because at first, “xmltype(cursor(…))” aggregated data as xmltype, and only then xmltable returns data.
But I use print_table for small amount of data only, and in case of when i want to see sample of data, i usually add limitation by rownum, which also convenient because it automatically changes optimizer mode with enabled parameter “_optimizer_rownum_pred_based_fkr” (it is default):

SQL> @param_ rownum

NAME                               VALUE   DEFLT  TYPE     DESCRIPTION
---------------------------------- ------- ------ -------- ------------------------------------------------------
_optimizer_rownum_bind_default     10      TRUE   number   Default value to use for rownum bind
_optimizer_rownum_pred_based_fkr   TRUE    TRUE   boolean  enable the use of first K rows due to rownum predicate
_px_rownum_pd                      TRUE    TRUE   boolean  turn off/on parallel rownum pushdown optimization

However, we can easily change the our query to make it optimally with a lot of data too:

select row_num
      ,t2.*
from 
   (select rownum row_num
         , column_value x
    from table(xmlsequence(cursor( &1 )))
   ) t1
  ,xmltable( '/ROW/*'
             passing t1.x
             columns
                col_num for ordinality
               ,col_name  varchar2(30) path 'name()'
               ,col_value varchar2(100) path '.'
      )(+) t2;

Lets test it with pipelined function which will pipe rows infinitely and log count of fetched rows:

-- drop table xt_log purge;
-- drop function f_infinite;

create table xt_log(n int);

create function f_infinite 
   return sys.ku$_objnumset pipelined 
as
   i int:=0;
   pragma autonomous_transaction;
begin
   loop 
      i:=i+1;
      insert into xt_log values(i);
      commit;
      pipe row(i);
   end loop;

exception 
   when NO_DATA_NEEDED then
      commit;
end;
/

And look final test:

SQL> select * from xt_log;

no rows selected

SQL> @print_table2 "select * from table(f_infinite)"
Press Enter to view next row...


   ROW_NUM    COL_NUM COL_NAME                       COL_VALUE
---------- ---------- ------------------------------ -----------
         1          1 COLUMN_VALUE                   1
Press Enter to view next row...


   ROW_NUM    COL_NUM COL_NAME                       COL_VALUE
---------- ---------- ------------------------------ -----------
         2          1 COLUMN_VALUE                   2
Press Enter to view next row...


   ROW_NUM    COL_NUM COL_NAME                       COL_VALUE
---------- ---------- ------------------------------ -----------
         3          1 COLUMN_VALUE                   3
Press Enter to view next row...


   ROW_NUM    COL_NUM COL_NAME                       COL_VALUE
---------- ---------- ------------------------------ -----------
         4          1 COLUMN_VALUE                   4
Press Enter to view next row...

   ROW_NUM    COL_NUM COL_NAME                       COL_VALUE
         5          1 COLUMN_VALUE                   5
Press Enter to view next row...


6 rows selected.
-------------------------------
SQL> select * from xt_log;

         N
----------
         1
         2
         3
         4
         5
         6
         7

7 rows selected.

So we got what we wanted!

PS. Full scripts:
1. Simple: print_table.sql
2. For big queries: print_table2.sql