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Oracle SQL: displaying multiple column values per row

Oracle Tips by Burleson Consulting


Until 11g, Oracle SQL did not have a direct mechanism for allowing multiple values from the same column to be displayed in the same row of output.  SQL is designed not to disallow repeating values on a single line of output, but Oracle has several tricks for allowing repeating groups of same-column values on a single line of output.  For example, assume that we need to display all degrees for an employee on a single row of SQL*Plus output:

Jones:  BA Art History, MBA in Finance, PhD in business
Smith:  BS in computer science
Baker:  BBA in Business administration, MS in computer science

Approaches to display many columns on one line of output

Let's take a look at how we can consolidate multiple values into a single-row display.

For using native SQL to place multiple rows onto one row, see my notes on converting multiple rows onto a single column:

Non SQL approaches:

  • Download data into Excel Pivot tables
  • The Oracle 9i xmlagg function
  • Write a PL/SQL function 

Let's look at each method to consolidate data from multiple table rows onto a single row.

Download data into Excel spreadsheet pivot table

Excel spreadsheets are a great way to pivot and analyze Oracle data, and tools like Excel-DB provide a fast API for downloading Oracle data into spreadsheets. Using Excel pivot tables with Oracle data is a fast, easy way to use Oracle business intelligence without buying expensive OLAP solutions (Hyperion, Oracle BI Suite).  Here is an example.

Oracle 9i xmlagg

In Oracle 9i we can use the xmlagg function to aggregate multiple rows onto one column:

select
   deptno,
   rtrim (xmlagg (xmlelement (e, ename || ',')).extract ('//text()'), ',') enames
from
   emp
group by
   deptno
;

    DEPTNO ENAMES                                 
---------- ----------------------------------------
        10 CLARK,MILLER,KING                      
        20 SMITH,FORD,ADAMS,SCOTT,JONES           
        30 ALLEN,JAMES,TURNER,BLAKE,MARTIN,WARD 

11g within group SQL

In Oracle 11g, we have the within group SQL clause to pivot multiple rows onto a single row.  We also a have direct SQL mechanism for non first-normal form SQL display. This allows multiple table column values to be displayed in a single column, using the listagg built-in function :

select
   deptno,
   listagg (ename, ',')
WITHIN GROUP
(ORDER BY ename) enames
FROM
   emp
GROUP BY
   deptno

    DEPTNO ENAMES                                           
---------- --------------------------------------------------
        10 CLARK,KING,MILLER                                
        20 ADAMS,FORD,JONES,SCOTT,SMITH                
        30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD 

Write a PL/SQL function

You can write a PL/SQL function to display multiple rows values on a single line.  Martin Chadderton has written a Pl/SQL function called "stragg" that you can define to display multiple SQL rows on one single line.  Once defined, you embed the function within your SQL to display your output on a single line:

select stragg(ename) from emp;

Smith, Jones, Baker

Use a user-defined rowtocol function to convert the rows to columns:

CREATE OR REPLACE  FUNCTION
   rowtocol( p_slct IN VARCHAR2, p_dlmtr IN VARCHAR2 DEFAULT ',' ) RETURN VARCHAR2

    AUTHID CURRENT_USER AS

 TYPE c_refcur IS REF CURSOR;

    lc_str VARCHAR2(4000);
    lc_colval VARCHAR2(4000);
    c_dummy c_refcur;
    l number;

    BEGIN

    OPEN c_dummy FOR p_slct;

    LOOP
    FETCH c_dummy INTO lc_colval;

    EXIT WHEN c_dummy%NOTFOUND;

    lc_str := lc_str || p_dlmtr || lc_colval;

    END LOOP;

    CLOSE c_dummy;

    RETURN SUBSTR(lc_str,2);

    /*
    EXCEPTION
    WHEN OTHERS THEN
    lc_str := SQLERRM;
    IF c_dummy%ISOPEN THEN
    CLOSE c_dummy;
    END IF;
    RETURN lc_str;
    */
    END;
    /


SELECT DISTINCT
   a.job,
   rowtocol(
    'SELECT ename
     FROM emp
     WHERE
     job = ' || '''' || a.job || '''' || ' ORDER BY ename')
     AS Employees

Use the SYS_CONNECT_BY_PATH Operator

This article by Younes Naguib describes how to display multiple values from a single column in a single output row.  In his example, he displays multiple values of the last name column on a single row.  Note his use of the sys_connect_by_path and over operators:

select
   deptno,
   substr(SYS_CONNECT_BY_PATH(lname, ','),2) name_list
from
   (
   select
     lname,
     deptno,
     count(*) OVER ( partition by deptno ) cnt,
     ROW_NUMBER () OVER ( partition by deptno order by lname) seq
   from
     igribun.emp
   where
     deptno is not null)
where
   seq=cnt
start with
   seq=1
connect by prior
   seq+1=seq
and prior
   deptno=deptno;

DEPTNO NAME_LIST
1      Komers,Mokrel,Stenko
2      Hung,Tong
3      Hamer
4      Mansur

Use a Cross join

Matt contributed this handy SQL techniques to pivot one row of several columns into a single column with several row, using the Oracle Cross join syntax.  Matt notes that the Cross join "has other uses in conjunction with a WHERE clause to create triangular result sets for rolling totals etc (though thanks to analytic functions those things are very nice and easy)".

SELECT
  ite,
  case
    when ite = 'item1' then item1
    when ite = 'item2' then item2
    when ite = 'item3' then item3
  end as val
FROM
(
  SELECT
    pivoter.ite,
    item1,
    item2,
    item3
  FROM
    someTable
    CROSS JOIN
    (
      select 'item1' as ite from dual
      UNION ALL
      select 'item2' as ite from dual
      UNION ALL
      select 'item3' as ite from dual
    )pivoter
)

Oracle analytic Lag-Over Function

Analytic functions have a pronounced performance improvement since they avoid an expensive self-join and only make one full-table scan to get the results.  This site shows an example of using the Oracle LAG function to display multiple rows on a single column:

SELECT   
   ename,  
   hiredate,sal,LAG (sal, 1, 0)  
   OVER (ORDER BY hiredate) AS PrevSal
FROM   
   emp
WHERE
    job = 'CLERK';

SQL Pivot Operator

The SQL pivot operator allows you to take multiple rows and display them on a single line.

select *
from
  (select fk_department
   from employee)
   pivot
    (count(fk_department)
      for fk_department in ('INT', 'WEL', 'CEN', 'POL'));

'INT'         'WEL'       'CEN'     'POL'                                                                            
----------    ----------   ----------  -------
        7            6            0          8    
  

Oracle SQL CASE statement

Use the CASE statement to create a crosstab to convert the rows to columns.  Below, the Oracle CASE function to create a "crosstab" of the results, such as this example from SearchOracle:

select Sales.ItemKey 
     , sum(Sales.QtySold)   as Qty 
     , sum(
         case when OH.MOHClass = 'Fixed'
              then OH.Amt
              else .00 end ) as MOHFixed 
     , sum(
         case when OH.MOHClass = 'Var'
              then OH.Amt
              else .00 end ) as MOHVar
     , sum(
         case when OH.MOHClass = 'Cap'
              then OH.Amt
              else .00 end ) as MOHCap
  from Sales
left outer
  join OH
    on Sales.ItemKey = OH.ItemKey
group
    by Sales.ItemKey

 

My Notes:

For more SQL tips and tricks, see the book "Easy Oracle SQL".  Also see these related notes on SQL output display consolidation:

 
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