Rollups, Cubes, Grouping Sets and their inner working All About Grouping November 23, 2018 Rollups, Cubes, Grouping Sets and their inner working Rob van Wijk

Who am I Database application developer 14 years with Oracle products Rob van Wijk Database application developer 14 years with Oracle products Utrecht November 23, 2018

All About Grouping Introduction GROUPING SETS ROLLUP CUBE Topics Introduction GROUPING SETS ROLLUP CUBE Combining and calculating Supporting functions Inner working November 23, 2018

All About Grouping Introduction aog1.sql November 23, 2018

All About Grouping GROUP BY expr1, …, exprn ≡ GROUP BY GROUPING SETS aog2.sql November 23, 2018

( (expr11, …, expr1n), …, (exprx1, …, exprxm) ) All About Grouping GROUPING SETS (2) GROUP BY GROUPING SETS ( (expr11, …, expr1n), …, (exprx1, …, exprxm) ) ≡ GROUP BY expr11, … expr1n UNION ALL … GROUP BY exprx1, …, exprxm aog3.sql November 23, 2018

All About Grouping GROUP BY ROLLUP ( set1, …, setn ) ≡ GROUP BY GROUPING SETS ( (set1, …, setn), (set1, …, setn-1), …, set1, () ) November 23, 2018

leads to N+1 GROUPING SETS All About Grouping ROLLUP (2) ROLLUP (set1, …, setN) with N ≥ 1 leads to N+1 GROUPING SETS November 23, 2018

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 November 23, 2018

All About Grouping GROUP BY CUBE ( set1, …, setn ) ≡ GROUP BY GROUPING SETS (all possible combinations between () and (set1, …, setn) ) November 23, 2018

leads to 2N GROUPING SETS All About Grouping CUBE (2) CUBE (set1, …, setN) with N ≥ 1 leads to 2N GROUPING SETS November 23, 2018

Follows Pascal’s triangle All About Grouping CUBE (3) Follows Pascal’s triangle 0 sets X 1 set 2 sets 3 sets 4 sets November 23, 2018

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 November 23, 2018

GROUP BY deptno, ROLLUP(empno) All About Grouping Combining and calculating (1) GROUP BY deptno, ROLLUP(empno) ? November 23, 2018

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, () ) November 23, 2018

All About Grouping Cartesian product ! GROUP BY deptno, ROLLUP(empno) Combining and calculating (3) Cartesian product ! GROUP BY deptno, ROLLUP(empno) ≡ GROUP BY GROUPING SETS (deptno) , GROUPING SETS ( (empno), () ) GROUP BY GROUPING SETS ( (deptno,empno), (deptno) ) aog6.sql November 23, 2018

All About Grouping Question: Combining and calculating (4) Question: How many grouping sets does the clause below yield? GROUP BY ROLLUP(deptno,job) , CUBE(mgr,hiredate) Answer: 3 * 4 = 12 aog7.sql November 23, 2018

All About Grouping GROUPING GROUPING_ID GROUP_ID aog8.sql Supporting functions GROUPING GROUPING_ID GROUP_ID aog8.sql November 23, 2018

All About Grouping SORT GROUP BY versus HASH GROUP BY Inner working November 23, 2018

+ + 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 November 23, 2018

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 November 23, 2018

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 November 23, 2018

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 November 23, 2018

All About Grouping Questions? November 23, 2018

Thanks for your attention! Blog: http://rwijk.blogspot.com All About Grouping Thanks for your attention! Email: rwijk72@gmail.com Blog: http://rwijk.blogspot.com November 23, 2018