Home > DBA, Oracle, SQL > The way you write your query matters: Performance comparison between CONNECT BY and recursive subquery factoring

The way you write your query matters: Performance comparison between CONNECT BY and recursive subquery factoring


I was asked to compare the performance of traditional CONNECT BY syntax with recursive subquery factoring (a.k.a. recursive common table expressions) but I only have part of the answer. To summarize my answer, the CONNECT BY NO FILTERING and CONNECT BY WITHOUT FILTERING strategies are not available for queries that use recursive subquery factoring. These strategies require fewer buffer gets and it appears that Oracle builds structures that allow it to perform the recursion without needing additional buffer gets after the first pass through the data set. These strategies may therefore be more efficient for small data sets but I don’t have the exact details of how exactly they work and would appreciate any insights that anybody can provide. These examples are further evidence that the way you write your query has performance implications. However, Dan Tow pointed out some confusing aspects of CONNECT BY syntax to me and therefore I recommend recursive subquery factoring for general use because of its greater clarity (and greater generality), performance implications notwithstanding.

Consider the well-known example of the employee hierarchy.

select
  rpad(' ', 2 * (level - 1)) || first_name || ' ' || last_name as name,
  emp.hire_date
from employees emp
start with emp.manager_id is null
connect by emp.manager_id = prior emp.employee_id
order siblings by hire_date;

The recursive subquery equivalent is extremely verbose in comparison. “RCTE” in the query below stands for “recursive common table expression.” Refer to my previous article I Heart Recursive Subquery Factoring (Recursive Common Table Expressions for a detailed explanation of such queries.

with rcte(lvl, employee_id, first_name, last_name, hire_date) as
(
-- anchor member
select
  1 as lvl,
  emp.employee_id,
  emp.first_name,
  emp.last_name,
  emp.hire_date
from employees emp
where emp.manager_id is null

union all

-- recursive member
select
  rcte.lvl + 1 as lvl,
  emp.employee_id,
  emp.first_name,
  emp.last_name,
  emp.hire_date
from
  rcte,
  employees emp
where rcte.employee_id = emp.manager_id
)
search depth first by hire_date set rank
select
  rpad(' ', 2 * (lvl - 1)) || first_name || ' ' || last_name as name,
  hire_date
from rcte;

Here is the execution plan for the above recursive subquery. It is a UNION ALL (step Id 2) of the TABLE ACCESS FULL operation (step Id 3) which retrieves the starting data set and the NESTED LOOPS operation (step Id 4) which retrieves initial rows.

SQL_ID  42cthn2bdc7s8, child number 0

Plan hash value: 3762696923

----------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                               | Name           | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |
----------------------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                        |                |      1 |        |       |     8 (100)|          |    107 |00:00:00.05 |      23 |
|   1 |  VIEW                                   |                |      1 |      7 |   336 |     8  (13)| 00:00:01 |    107 |00:00:00.05 |      23 |
|   2 |   UNION ALL (RECURSIVE WITH) DEPTH FIRST|                |      1 |        |       |            |          |    107 |00:00:00.05 |      23 |
|*  3 |    TABLE ACCESS FULL                    | EMPLOYEES      |      1 |      1 |    61 |     3   (0)| 00:00:01 |      1 |00:00:00.01 |       7 |
|   4 |    NESTED LOOPS                         |                |      4 |        |       |            |          |    106 |00:00:00.02 |      16 |
|   5 |     NESTED LOOPS                        |                |      4 |      6 |   522 |     4   (0)| 00:00:01 |    106 |00:00:00.01 |       5 |
|   6 |      RECURSIVE WITH PUMP                |                |      4 |        |       |            |          |    107 |00:00:00.01 |       0 |
|*  7 |      INDEX RANGE SCAN                   | EMP_MANAGER_IX |    107 |      6 |       |     0   (0)|          |    106 |00:00:00.01 |       5 |
|   8 |     TABLE ACCESS BY INDEX ROWID         | EMPLOYEES      |    106 |      6 |   366 |     1   (0)| 00:00:01 |    106 |00:00:00.04 |      11 |
----------------------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   3 - filter("EMP"."MANAGER_ID" IS NULL)
   7 - access("RCTE"."EMPLOYEE_ID"="EMP"."MANAGER_ID")

Three different execution strategies are available for the traditional CONNECT BY syntax. In the examples below, I used the mysteriously named NO_CONNECT_BY_FILTERING, NO_CONNECT_BY_COMBINE_SW, and CONNECT_BY_FILTERING hints respectively to force the optimizer to use the strategies I wanted. I can’t explain the allusions to filtering in the names so any insights would be appreciated. My best guess is that NO_CONNECT_BY_COMBINE_SW means that the optimizer will not include the cost of the START WITH clause in its costing calculations. The CONNECT_BY_FILTERING strategy is very similar to the strategy used above for recursive subquery factoring.

Here is the execution plan for the traditional query with the addition of the NO_CONNECT_BY_FILTERING hint. The number of buffer gets is only 7 and the employee table is touched only once implying that Oracle has created a hashed structure to perform the recursion.

SQL_ID  2xfgzbz36s2qu, child number 0

Plan hash value: 1986864582

-----------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                               | Name      | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |
-----------------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                        |           |      1 |        |       |     4 (100)|          |    107 |00:00:00.01 |       7 |
|*  1 |  CONNECT BY NO FILTERING WITH START-WITH|           |      1 |        |       |            |          |    107 |00:00:00.01 |       7 |
|   2 |   TABLE ACCESS FULL                     | EMPLOYEES |      1 |    107 |  6527 |     3   (0)| 00:00:01 |    107 |00:00:00.01 |       7 |
-----------------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("EMP"."MANAGER_ID"=PRIOR NULL)
       filter("EMP"."MANAGER_ID" IS NULL)

Here is the execution plan for the traditional query with the addition of the NO_CONNECT_BY_COMBINE_SW hint. There are two passes through the Employees table. The number of buffer gets is 14. Based on the values in the Starts and A-Rows column, it appears that Oracle has created a hashed structure from the results of the second pass. Therefore, this strategy may not offer any advantages over the NO_CONNECT_BY_FILTERING strategy.

SQL_ID  a9bux4t6t76qw, child number 0

Plan hash value: 1497856380

------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                    | Name      | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |
------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT             |           |      1 |        |       |     7 (100)|          |    107 |00:00:00.01 |      14 |
|*  1 |  CONNECT BY WITHOUT FILTERING|           |      1 |        |       |            |          |    107 |00:00:00.01 |      14 |
|*  2 |   TABLE ACCESS FULL          | EMPLOYEES |      1 |      1 |    61 |     3   (0)| 00:00:01 |      1 |00:00:00.01 |       7 |
|   3 |   TABLE ACCESS FULL          | EMPLOYEES |      1 |    107 |  6527 |     3   (0)| 00:00:01 |    107 |00:00:00.01 |       7 |
------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("EMP"."MANAGER_ID"=PRIOR NULL)
   2 - filter("EMP"."MANAGER_ID" IS NULL)

Here is the execution plan for the traditional query with the addition of the CONNECT_BY_FILTERING hint. The execution plan is now very similar to that in the case of the recursive subquery factoring example. Once again there is a TABLE ACCESS FULL (step Id 2) to retrieve the starting data set and a NESTED LOOPS operation (step Id 3) to retrieve additional rows. The number of buffer gets (22) is almost identical to that of the recursive subquery factoring case (23).

SQL_ID  24wb2xqwkrm4x, child number 0

Plan hash value: 2829436659

------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name           | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |
------------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |                |      1 |        |       |     8 (100)|          |    107 |00:00:00.01 |      22 |
|*  1 |  CONNECT BY WITH FILTERING    |                |      1 |        |       |            |          |    107 |00:00:00.01 |      22 |
|*  2 |   TABLE ACCESS FULL           | EMPLOYEES      |      1 |      1 |    61 |     3   (0)| 00:00:01 |      1 |00:00:00.01 |       7 |
|   3 |   NESTED LOOPS                |                |      4 |      6 |   444 |     4   (0)| 00:00:01 |    106 |00:00:00.01 |      15 |
|   4 |    CONNECT BY PUMP            |                |      4 |        |       |            |          |    107 |00:00:00.01 |       0 |
|   5 |    TABLE ACCESS BY INDEX ROWID| EMPLOYEES      |    107 |      6 |   366 |     1   (0)| 00:00:01 |    106 |00:00:00.01 |      15 |
|*  6 |     INDEX RANGE SCAN          | EMP_MANAGER_IX |    107 |      6 |       |     0   (0)|          |    106 |00:00:00.01 |       5 |
------------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("EMP"."MANAGER_ID"=PRIOR NULL)
   2 - filter("EMP"."MANAGER_ID" IS NULL)
   6 - access("EMP"."MANAGER_ID"="connect$_by$_pump$_002"."prior emp.employee_id ")

Dan Tow pointed out some confusing aspects of CONNECT BY syntax to me and therefore I recommend recursive subquery factoring for general use because of its clarity. Consider the following two queries; at first glance they appear to be functionally identical but their results prove otherwise. The first uses INNER JOIN while the second does not. Both include the condition “dep.department_name = ‘Sales’.”

-- INNER JOIN version
select
  rpad(' ', 2 * (level - 1)) || first_name || ' ' || last_name as name,
  emp.hire_date,
  dep.department_name
from
  employees emp
  inner join departments dep on (emp.department_id = dep.department_id and dep.department_name = 'Sales')
-- No START WITH clause is required in this example
connect by emp.manager_id = prior emp.employee_id
order siblings by hire_date;

-- Traditional version
select
  rpad(' ', 2 * (level - 1)) || first_name || ' ' || last_name as name,
  emp.hire_date,
  dep.department_name
from
  employees emp,
  departments dep
where emp.department_id = dep.department_id
and dep.department_name = 'Sales'
-- No START WITH clause is required in this example
connect by emp.manager_id = prior emp.employee_id
order siblings by hire_date;

Here are the execution plan and results of the INNER JOIN version. 63 rows are produced. The condition “dep.department_name = ‘Sales’” is checked at step Id 4.

SQL_ID  0gpmzjr5zcybv, child number 0

Plan hash value: 849430486

---------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                     | Name        | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |
---------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |             |      1 |        |       |     4 (100)|          |     63 |00:00:00.01 |     117 |
|*  1 |  CONNECT BY WITHOUT FILTERING |             |      1 |        |       |            |          |     63 |00:00:00.01 |     117 |
|   2 |   NESTED LOOPS                |             |      1 |     10 |  1040 |     3   (0)| 00:00:01 |     34 |00:00:00.01 |     117 |
|   3 |    TABLE ACCESS FULL          | EMPLOYEES   |      1 |    107 |  7918 |     3   (0)| 00:00:01 |    107 |00:00:00.01 |       7 |
|*  4 |    TABLE ACCESS BY INDEX ROWID| DEPARTMENTS |    107 |      1 |    30 |     0   (0)|          |     34 |00:00:00.01 |     110 |
|*  5 |     INDEX UNIQUE SCAN         | DEPT_ID_PK  |    107 |      1 |       |     0   (0)|          |    106 |00:00:00.01 |       4 |
---------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("EMP"."MANAGER_ID"=PRIOR NULL)
   4 - filter("DEP"."DEPARTMENT_NAME"='Sales')
   5 - access("EMP"."DEPARTMENT_ID"="DEP"."DEPARTMENT_ID")

NAME                           HIRE_DATE DEPARTMENT_NAME
------------------------------ --------- ------------------------------
John Russell                   01-OCT-96 Sales
  Peter Tucker                 30-JAN-97 Sales
  David Bernstein              24-MAR-97 Sales
  Peter Hall                   20-AUG-97 Sales
  Christopher Olsen            30-MAR-98 Sales
  Nanette Cambrault            09-DEC-98 Sales
  Oliver Tuvault               23-NOV-99 Sales
Karen Partners                 05-JAN-97 Sales
  Janette King                 30-JAN-96 Sales
  Patrick Sully                04-MAR-96 Sales
  Allan McEwen                 01-AUG-96 Sales
  Lindsey Smith                10-MAR-97 Sales
  Louise Doran                 15-DEC-97 Sales
  Sarath Sewall                03-NOV-98 Sales
Alberto Errazuriz              10-MAR-97 Sales
  Clara Vishney                11-NOV-97 Sales
  Danielle Greene              19-MAR-99 Sales
  Mattea Marvins               24-JAN-00 Sales
  David Lee                    23-FEB-00 Sales
  Sundar Ande                  24-MAR-00 Sales
  Amit Banda                   21-APR-00 Sales
Gerald Cambrault               15-OCT-99 Sales
  Lisa Ozer                    11-MAR-97 Sales
  Tayler Fox                   24-JAN-98 Sales
  Harrison Bloom               23-MAR-98 Sales
  William Smith                23-FEB-99 Sales
  Elizabeth Bates              24-MAR-99 Sales
  Sundita Kumar                21-APR-00 Sales
Eleni Zlotkey                  29-JAN-00 Sales
  Ellen Abel                   11-MAY-96 Sales
  Alyssa Hutton                19-MAR-97 Sales
  Jonathon Taylor              24-MAR-98 Sales
  Jack Livingston              23-APR-98 Sales
  Charles Johnson              04-JAN-00 Sales
Peter Tucker                   30-JAN-97 Sales
David Bernstein                24-MAR-97 Sales
Peter Hall                     20-AUG-97 Sales
Christopher Olsen              30-MAR-98 Sales
Nanette Cambrault              09-DEC-98 Sales
Oliver Tuvault                 23-NOV-99 Sales
Janette King                   30-JAN-96 Sales
Patrick Sully                  04-MAR-96 Sales
Allan McEwen                   01-AUG-96 Sales
Lindsey Smith                  10-MAR-97 Sales
Louise Doran                   15-DEC-97 Sales
Sarath Sewall                  03-NOV-98 Sales
Clara Vishney                  11-NOV-97 Sales
Danielle Greene                19-MAR-99 Sales
Mattea Marvins                 24-JAN-00 Sales
David Lee                      23-FEB-00 Sales
Sundar Ande                    24-MAR-00 Sales
Amit Banda                     21-APR-00 Sales
Lisa Ozer                      11-MAR-97 Sales
Tayler Fox                     24-JAN-98 Sales
Harrison Bloom                 23-MAR-98 Sales
William Smith                  23-FEB-99 Sales
Elizabeth Bates                24-MAR-99 Sales
Sundita Kumar                  21-APR-00 Sales
Ellen Abel                     11-MAY-96 Sales
Alyssa Hutton                  19-MAR-97 Sales
Jonathon Taylor                24-MAR-98 Sales
Jack Livingston                23-APR-98 Sales
Charles Johnson                04-JAN-00 Sales

63 rows selected.

Here are the execution plan and results of the more traditional version. 97 rows are produced instead of 63. The condition “dep.department_name = ‘Sales’” is checked at step Id 1.

SQL_ID  156g27gqtx4qu, child number 0

Plan hash value: 658926182

----------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                      | Name        | Starts | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | A-Rows |   A-Time   | Buffers |
----------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |             |      1 |        |       |     4 (100)|          |     97 |00:00:00.01 |     117 |
|*  1 |  FILTER                        |             |      1 |        |       |            |          |     97 |00:00:00.01 |     117 |
|*  2 |   CONNECT BY WITHOUT FILTERING |             |      1 |        |       |            |          |    312 |00:00:00.05 |     117 |
|   3 |    NESTED LOOPS                |             |      1 |    106 | 11024 |     3   (0)| 00:00:01 |    106 |00:00:00.01 |     117 |
|   4 |     TABLE ACCESS FULL          | EMPLOYEES   |      1 |    107 |  7918 |     3   (0)| 00:00:01 |    107 |00:00:00.01 |       7 |
|   5 |     TABLE ACCESS BY INDEX ROWID| DEPARTMENTS |    107 |      1 |    30 |     0   (0)|          |    106 |00:00:00.01 |     110 |
|*  6 |      INDEX UNIQUE SCAN         | DEPT_ID_PK  |    107 |      1 |       |     0   (0)|          |    106 |00:00:00.01 |       4 |
----------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("DEP"."DEPARTMENT_NAME"='Sales')
   2 - access("EMP"."MANAGER_ID"=PRIOR NULL)
   6 - access("EMP"."DEPARTMENT_ID"="DEP"."DEPARTMENT_ID")

NAME                           HIRE_DATE DEPARTMENT_NAME
------------------------------ --------- ------------------------------
John Russell                   01-OCT-96 Sales
  Peter Tucker                 30-JAN-97 Sales
  David Bernstein              24-MAR-97 Sales
  Peter Hall                   20-AUG-97 Sales
  Christopher Olsen            30-MAR-98 Sales
  Nanette Cambrault            09-DEC-98 Sales
  Oliver Tuvault               23-NOV-99 Sales
Karen Partners                 05-JAN-97 Sales
  Janette King                 30-JAN-96 Sales
  Patrick Sully                04-MAR-96 Sales
  Allan McEwen                 01-AUG-96 Sales
  Lindsey Smith                10-MAR-97 Sales
  Louise Doran                 15-DEC-97 Sales
  Sarath Sewall                03-NOV-98 Sales
Alberto Errazuriz              10-MAR-97 Sales
  Clara Vishney                11-NOV-97 Sales
  Danielle Greene              19-MAR-99 Sales
  Mattea Marvins               24-JAN-00 Sales
  David Lee                    23-FEB-00 Sales
  Sundar Ande                  24-MAR-00 Sales
  Amit Banda                   21-APR-00 Sales
Gerald Cambrault               15-OCT-99 Sales
  Lisa Ozer                    11-MAR-97 Sales
  Tayler Fox                   24-JAN-98 Sales
  Harrison Bloom               23-MAR-98 Sales
  William Smith                23-FEB-99 Sales
  Elizabeth Bates              24-MAR-99 Sales
  Sundita Kumar                21-APR-00 Sales
Eleni Zlotkey                  29-JAN-00 Sales
  Ellen Abel                   11-MAY-96 Sales
  Alyssa Hutton                19-MAR-97 Sales
  Jonathon Taylor              24-MAR-98 Sales
  Jack Livingston              23-APR-98 Sales
  Charles Johnson              04-JAN-00 Sales
Peter Tucker                   30-JAN-97 Sales
David Bernstein                24-MAR-97 Sales
Peter Hall                     20-AUG-97 Sales
Christopher Olsen              30-MAR-98 Sales
Nanette Cambrault              09-DEC-98 Sales
Oliver Tuvault                 23-NOV-99 Sales
Janette King                   30-JAN-96 Sales
Patrick Sully                  04-MAR-96 Sales
Allan McEwen                   01-AUG-96 Sales
Lindsey Smith                  10-MAR-97 Sales
Louise Doran                   15-DEC-97 Sales
Sarath Sewall                  03-NOV-98 Sales
Clara Vishney                  11-NOV-97 Sales
Danielle Greene                19-MAR-99 Sales
Mattea Marvins                 24-JAN-00 Sales
David Lee                      23-FEB-00 Sales
Sundar Ande                    24-MAR-00 Sales
Amit Banda                     21-APR-00 Sales
Lisa Ozer                      11-MAR-97 Sales
Tayler Fox                     24-JAN-98 Sales
Harrison Bloom                 23-MAR-98 Sales
William Smith                  23-FEB-99 Sales
Elizabeth Bates                24-MAR-99 Sales
Sundita Kumar                  21-APR-00 Sales
Ellen Abel                     11-MAY-96 Sales
Alyssa Hutton                  19-MAR-97 Sales
Jonathon Taylor                24-MAR-98 Sales
Jack Livingston                23-APR-98 Sales
Charles Johnson                04-JAN-00 Sales
  John Russell                 01-OCT-96 Sales
    Peter Tucker               30-JAN-97 Sales
    David Bernstein            24-MAR-97 Sales
    Peter Hall                 20-AUG-97 Sales
    Christopher Olsen          30-MAR-98 Sales
    Nanette Cambrault          09-DEC-98 Sales
    Oliver Tuvault             23-NOV-99 Sales
  Karen Partners               05-JAN-97 Sales
    Janette King               30-JAN-96 Sales
    Patrick Sully              04-MAR-96 Sales
    Allan McEwen               01-AUG-96 Sales
    Lindsey Smith              10-MAR-97 Sales
    Louise Doran               15-DEC-97 Sales
    Sarath Sewall              03-NOV-98 Sales
  Alberto Errazuriz            10-MAR-97 Sales
    Clara Vishney              11-NOV-97 Sales
    Danielle Greene            19-MAR-99 Sales
    Mattea Marvins             24-JAN-00 Sales
    David Lee                  23-FEB-00 Sales
    Sundar Ande                24-MAR-00 Sales
    Amit Banda                 21-APR-00 Sales
  Gerald Cambrault             15-OCT-99 Sales
    Lisa Ozer                  11-MAR-97 Sales
    Tayler Fox                 24-JAN-98 Sales
    Harrison Bloom             23-MAR-98 Sales
    William Smith              23-FEB-99 Sales
    Elizabeth Bates            24-MAR-99 Sales
    Sundita Kumar              21-APR-00 Sales
  Eleni Zlotkey                29-JAN-00 Sales
    Ellen Abel                 11-MAY-96 Sales
    Alyssa Hutton              19-MAR-97 Sales
    Jonathon Taylor            24-MAR-98 Sales
    Jack Livingston            23-APR-98 Sales
    Charles Johnson            04-JAN-00 Sales

97 rows selected.

This is not a bug. According to the SQL Language Reference:

If the query contains a WHERE clause without a join, then Oracle eliminates all rows from the hierarchy that do not satisfy the condition of the WHERE clause. Oracle evaluates this condition for each row individually, rather than removing all the children of a row that does not satisfy the condition.

To make things clearer, here is the recursive subquery factoring version of the above query. Notice that the condition “department_name = ‘Sales’” has been placed outside the recursive subquery.

with rcte(lvl, employee_id, first_name, last_name, hire_date, department_name) as
(
select
  1 as lvl,
  emp.employee_id,
  emp.first_name,
  emp.last_name,
  emp.hire_date,
  dep.department_name
from
  employees emp,
  departments dep
where emp.department_id = dep.department_id

union all

select
  rcte.lvl + 1 as lvl,
  emp.employee_id,
  emp.first_name,
  emp.last_name,
  emp.hire_date,
  dep.department_name
from
  rcte,
  employees emp,
  departments dep
where rcte.employee_id = emp.manager_id
and emp.department_id = dep.department_id
)
search depth first by hire_date set rank
select
  rpad(' ', 2 * (lvl - 1)) || first_name || ' ' || last_name as name,
  hire_date,
  department_name
from rcte
where department_name = 'Sales';

All the above examples were produced using Oracle Database 11g Release 2 and the Developer Days Virtual Machine.

Categories: DBA, Oracle, SQL
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