If you've never heard of or used Oracle analytic functions please read this article first. It's by far the best article I've read at explaining what analytic functions are and how to use them. The Oracle analytic function documentation can be found here.
RATIO_TO_REPORT
RATIO_TO_REPORT compares the current value against the sum of the other set of values. The following example shows the percentage of each employees salary when compared to the sum of their department's salary. You'll notice that you can calculate the same value using a different method (sal_dept_ratio2) which may be why I haven't seen RATIO_TO_REPORT used that often.
SELECT d.dname, e.ename, e.sal, round(ratio_to_report(sal) OVER (PARTITION BY e.deptno),2) sal_dept_ratio, round(sal / sum(e.sal) OVER (PARTITION BY e.deptno),2) sal_dept_ratio2 FROM emp e, dept d WHERE e.deptno = d.deptno; -- Result DNAME ENAME SAL SAL_DEPT_RATIO SAL_DEPT_RATIO2 -------------- ---------- ---------- -------------- --------------- ACCOUNTING CLARK 2450 .28 .28 ACCOUNTING MILLER 1300 .15 .15 ACCOUNTING KING 5000 .57 .57 RESEARCH FORD 3000 .28 .28 RESEARCH SCOTT 3000 .28 .28 RESEARCH JONES 2975 .27 .27 RESEARCH SMITH 800 .07 .07 RESEARCH ADAMS 1100 .1 .1 SALES WARD 1250 .13 .13 SALES MARTIN 1250 .13 .13 SALES TURNER 1500 .16 .16 SALES JAMES 950 .1 .1 SALES ALLEN 1600 .17 .17 SALES BLAKE 2850 .3 .3
NTH_VALUE
NTH_VALUE returns the nth row in the window clause. It's extremely important that you explicitly define the window or your values may not make sense. I'll write another post explaining this later. Update: NTH_VALUE Windowing Clause
The following example shows the 2nd highest salary in each department.
SELECT d.dname, e.ename, e.sal,
nth_value(e.sal, 2) OVER (
PARTITION BY e.deptno ORDER BY e.sal DESC
-- Don't forget to define the window
ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) sec_high_sal_dept
FROM emp e, dept d
WHERE e.deptno = d.deptno;
-- Result
DNAME ENAME SAL SEC_HIGH_SAL_DEPT
-------------- ---------- ---------- -----------------
ACCOUNTING KING 5000 2450
ACCOUNTING CLARK 2450 2450
ACCOUNTING MILLER 1300 2450
RESEARCH FORD 3000 3000
RESEARCH SCOTT 3000 3000
RESEARCH JONES 2975 3000
RESEARCH ADAMS 1100 3000
RESEARCH SMITH 800 3000
SALES BLAKE 2850 1600
SALES ALLEN 1600 1600
SALES TURNER 1500 1600
SALES WARD 1250 1600
SALES MARTIN 1250 1600
SALES JAMES 950 1600
LISTAGG
LISTAGG was a highly requested feature that was implemented in 11gR2. Overall LISTAGG allows you to group values in multiple rows and put them in a comma delimited column on one row.
The following example (which is not an analytic function) shows all the employees for each department:
SELECT d.dname, listagg(e.ename, ',') WITHIN GROUP (ORDER BY e.ename) dept_emp_list FROM emp e, dept d WHERE e.deptno = d.deptno GROUP BY d.dname; -- Result DNAME DEPT_EMP_LIST -------------- ---------------------------------------- ACCOUNTING CLARK,KING,MILLER RESEARCH ADAMS,FORD,JONES,SCOTT,SMITH SALES ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARDUsing the LISTAGG as an analytic function you can see each employee's colleagues in their department, including themselves.
SELECT d.dname, e.ename,
listagg(e.ename, ',') WITHIN GROUP (ORDER BY e.ename)
OVER (PARTITION BY e.deptno) dept_colleagues
FROM emp e, dept d
WHERE e.deptno = d.deptno;
-- Result
DNAME ENAME DEPT_COLLEAGUES
-------------- ---------- --------------------------------------
ACCOUNTING CLARK CLARK,KING,MILLER
ACCOUNTING KING CLARK,KING,MILLER
ACCOUNTING MILLER CLARK,KING,MILLER
RESEARCH ADAMS ADAMS,FORD,JONES,SCOTT,SMITH
RESEARCH FORD ADAMS,FORD,JONES,SCOTT,SMITH
RESEARCH JONES ADAMS,FORD,JONES,SCOTT,SMITH
RESEARCH SCOTT ADAMS,FORD,JONES,SCOTT,SMITH
RESEARCH SMITH ADAMS,FORD,JONES,SCOTT,SMITH
SALES ALLEN ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
SALES BLAKE ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
SALES JAMES ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
SALES MARTIN ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
SALES TURNER ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
SALES WARD ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
NTILE
NTILE allows you to divide your values into buckets and see which bucket the current row belongs to. For educational institutions this is a very good function to let students know that they're in the top x% of the class.
Update (12-Apr-2014): NTILE vs WIDTH_BOX describes the different ways to bucket data in Oracle. It also explains why SAL 1250 exists in both buckets 2 and 3.
The following example shows the 3 tiers (or buckets) of salaries across the entire company. It allows you to easily see who's in the top 33% of salaries.
SELECT d.dname, e.ename, e.sal, ntile (3) over (order by sal desc) three_tier_sal FROM emp e, dept d WHERE e.deptno = d.deptno; -- Result DNAME ENAME SAL THREE_TIER_SAL -------------- ---------- ---------- -------------- ACCOUNTING KING 5000 1 RESEARCH SCOTT 3000 1 RESEARCH FORD 3000 1 RESEARCH JONES 2975 1 SALES BLAKE 2850 1 ACCOUNTING CLARK 2450 2 SALES ALLEN 1600 2 SALES TURNER 1500 2 ACCOUNTING MILLER 1300 2 SALES WARD 1250 2 SALES MARTIN 1250 3 RESEARCH ADAMS 1100 3 SALES JAMES 950 3 RESEARCH SMITH 800 3
