1. Rollups, Cubes, Grouping Sets and their inner working
All About Grouping
January 2, 2019
Rollups, Cubes, Grouping Sets and their inner working
Rob van Wijk

2. Who am I Database application developer 14 years with Oracle products
Rob van Wijk
Database application developer
14 years with Oracle products
Utrecht
January 2, 2019

3. All About Grouping Introduction GROUPING SETS ROLLUP CUBE
Topics
Introduction
GROUPING SETS
ROLLUP
CUBE
Combining and calculating
Supporting functions
Inner working
January 2, 2019

4. All About Grouping
Introduction
aog1.sql
January 2, 2019

5. All About Grouping GROUP BY expr1, …, exprn ≡ GROUP BY GROUPING SETS
aog2.sql
January 2, 2019

6. All About Grouping GROUP BY GROUPING SETS ( set1, …, setx ) ≡
GROUP BY set1
UNION ALL …
GROUP BY setx
aog3.sql
January 2, 2019

7. All About Grouping GROUP BY ROLLUP ( set1, …, setn ) ≡
GROUP BY GROUPING SETS
( (set1 U … U setn), (set1 U … U setn-1), …, set1, () )
January 2, 2019

8. leads to N+1 GROUPING SETS
All About Grouping
ROLLUP (2)
ROLLUP (set1, …, setN)
with N ≥ 1
leads to N+1 GROUPING SETS
January 2, 2019

9. All About Grouping Example:
ROLLUP (3)
Example:
GROUP BY ROLLUP ( (deptno), (job,mgr), (empno) ) ≡
GROUP BY GROUPING SETS
( (deptno,job,mgr,empno)
, (deptno,job,mgr)
, (deptno)
, () )
aog4.sql
January 2, 2019

10. All About Grouping GROUP BY CUBE ( set1, …, setn ) ≡
GROUP BY GROUPING SETS
(all possible combinations between (set1 U … U setn) and () )
January 2, 2019

11. leads to 2N GROUPING SETS
All About Grouping
CUBE (2)
CUBE (set1, …, setN)
with N ≥ 1
leads to 2N GROUPING SETS
January 2, 2019

12. Follows Pascal’s triangle
All About Grouping
CUBE (3)
Follows Pascal’s triangle
0 sets X
1 set
2 sets
3 sets
4 sets
January 2, 2019

13. All About Grouping Example:
CUBE (4)
Example:
GROUP BY CUBE ( (deptno), (job,mgr), (empno) ) ≡
GROUP BY GROUPING SETS
( (deptno,job,mgr,empno)
, (deptno,job,mgr), (deptno,empno), (job,mgr,empno)
, (deptno), (job,mgr), (empno)
, () )
aog5.sql
January 2, 2019

14. GROUP BY deptno, ROLLUP(empno)
All About Grouping
Combining and calculating (1)
GROUP BY deptno, ROLLUP(empno) ?
January 2, 2019

15. All About Grouping GROUP BY deptno, ROLLUP(empno) ≡
Combining and calculating (2)
GROUP BY deptno, ROLLUP(empno) ≡
GROUP BY GROUPING SETS (deptno)
, GROUPING SETS ( empno, () )
January 2, 2019

16. All About Grouping Cartesian product !
Combining and calculating (3)
Cartesian product !
GROUP BY GROUPING SETS ( set1 , …, setX )
, GROUPING SETS ( setX+1 , …, setX+Y ) ≡
GROUP BY GROUPING SETS
(set1 U setX+1 , …,set1 U setX+Y
, …
, setX U setX+1 , …,setX U setX+Y )
January 2, 2019

17. All About Grouping GROUP BY deptno, ROLLUP(empno) ≡
Combining and calculating (4)
GROUP BY deptno, ROLLUP(empno) ≡
GROUP BY GROUPING SETS (deptno)
, GROUPING SETS ( (empno), () )
GROUP BY GROUPING SETS
( (deptno,empno), (deptno) )
aog6.sql
January 2, 2019

18. All About Grouping Question:
Combining and calculating (5)
Question:
How many grouping sets does the clause below yield?
GROUP BY ROLLUP(deptno,job)
, CUBE(mgr,hiredate)
Answer: 3 * 4 = 12
aog7.sql
January 2, 2019

19. GROUP BY deptno, ename, CUBE(empno,job,mgr)
All About Grouping
Combining and calculating (6)
GROUP BY
deptno
, ROLLUP(empno)
, CUBE(job,mgr)
, GROUPING SETS (ename) ≡
GROUP BY deptno, ename, CUBE(empno,job,mgr)
aog7a.sql
January 2, 2019

20. All About Grouping GROUPING GROUPING_ID GROUP_ID aog8.sql
Supporting functions
GROUPING
GROUPING_ID
GROUP_ID
aog8.sql
January 2, 2019

21. All About Grouping SORT GROUP BY versus HASH GROUP BY Inner working
January 2, 2019

22. + + All About Grouping aog9.sql Inner working: ROLLUP (deptno,empno)
incoming set
grouping set ( (deptno,empno) )
SORT GROUP BY 10
7782
2450
7839
5000
7934
1300 20
7369
800
7566
2975
7788
3000
7876
1100
7902 30
7499
1600
7521
1250
7654
7698
2850
7844
1500
7900
950
grouping set ( (deptno) ) + 10
NULL
8750 20
NULL
10875 30
NULL
9400
SORT GROUP BY
grouping set ( () ) +
NULL
29025
SORT GROUP BY
aog9.sql
January 2, 2019

23. All About Grouping aog10.sql Inner working: CUBE(deptno,job)
incoming set
14 rows
grouping set (deptno,job)
SORT GROUP BY
9 rows 36
rows
GENERATE CUBE
18 rows
SORT GROUP BY
aog10.sql
January 2, 2019

24. All About Grouping temporary input table SYS_TEMP_... temporary
Inner working: GROUPING SETS (1)
LOAD AS SELECT (into input table)
TABLE ACCESS FULL (EMP)
temporary
input table
SYS_TEMP_...
LOAD AS SELECT (into outputtable)
HASH GROUP BY
TABLE ACCESS FULL (input table)
iterate as much times as
there are grouping sets
temporary
output table
SYS_TEMP_...
TEMP TABLE TRANSFORMATION
VIEW
TABLE ACCESS FULL (output table)
aog11.sql
January 2, 2019

25. Optimize towards a ROLLUP or CUBE execution,
All About Grouping
Inner working: GROUPING SETS (2)
Optimize towards a ROLLUP or CUBE execution,
if possible?
aog12.sql
January 2, 2019

26. All About Grouping
Questions?
January 2, 2019

27. Thanks for your attention! Blog: http://rwijk.blogspot.com
All About Grouping
Thanks for your attention!
Blog:
January 2, 2019