Explore the power of analytic functions

Analytic functions are still underutilized among database developers. The goal of this publication is to demonstrate hidden opportunities to improve query performance by using analytic functions where traditional approach is still dominating.

Let’s consider a few examples. We will use Oracle’s traditional educational schema scott and its famous emp and dept tables.

Problem #1: Find all employees from the department where a top paid clerk works.

A quick look at the clerk records reveals the expected department (10):

SELECT deptno, job, sal
FROM scott.emp
WHERE job = 'CLERK'
ORDER BY sal DESC

Result:

DEPTNO	JOB	SAL
10	CLERK	1300
20	CLERK	1100
30	CLERK	950
20	CLERK	800

Traditional approach suggests finding the department (10) first and then the task becomes trivial:

SELECT ename, deptno, job, sal
FROM scott.emp
WHERE deptno IN (<department that we found>)

OK, that works, but now we need to produce a query that will get us that department number (of several ones if they all have top paid clerks).

There are many ways of finding a top record with and without analytic functions. If we don’t use analytic functions we will end up using two copies of the emp table as in the following example:

SELECT deptno
FROM scott.emp
WHERE job = 'CLERK'
  AND sal = (SELECT MAX(sal) FROM scott.emp WHERE job = 'CLERK')

or this:

SELECT a.deptno
FROM scott.emp a LEFT JOIN scott.emp b ON a.sal < b.sal
AND b.job = 'CLERK'
WHERE b.deptno IS NULL 
  AND a.job = 'CLERK'

The use of analytic functions reduces the number of table copies as we can get all the necessary details in a single table scan as in the following query:

WITH x AS (
SELECT deptno, MAX(sal) max_sal, RANK() OVER(ORDER BY MAX(sal) DESC) rk
FROM scott.emp
WHERE job = 'CLERK'
GROUP BY deptno
)
SELECT deptno
FROM x
WHERE rk = 1

Such SQL looks even shorter in databases, such as Snowflake and Terdata, that support QUALIFY clause in SELECT statement:

SELECT deptno
FROM scott.emp
WHERE job = 'CLERK'
GROUP BY deptno
QUALIFY RANK() OVER(ORDER BY MAX(sal) DESC) = 1

So a complete traditional approach will use 3 copies of the emp table as in the following query:

SELECT ename, deptno, job, sal
FROM scott.emp                                 -- copy #1
WHERE deptno IN (SELECT deptno
                 FROM scott.emp                -- copy #2
                 WHERE job = 'CLERK'
                   AND sal = (SELECT MAX(sal) 
                              FROM scott.emp   -- copy #3
                              WHERE job = 'CLERK')
                 )

Yes, it works, but what an overkill! Is it still possible to use a single emp table scan to solve this problem? The answer is YES:

WITH x AS (
SELECT ename, deptno, job, sal, 
       MAX(DECODE(job,'CLERK',sal)) OVER() max_sal_global,
       MAX(DECODE(job,'CLERK',sal)) OVER(PARTITION BY deptno) max_sal_dept
FROM scott.emp
)
SELECT ename, deptno, job, sal
FROM x
WHERE max_sal_global=max_sal_dept

And of course, in the Snowflake/Teradata SQL we would not even have to use a CTE (common table expression) , thanks to the QUALIFY clause.

MAX analytic functions combined with DECODE (CASE would work as well) here ignore all non-Clerk rows . The OVER clause gives us either department level top salary or global top salary value for the clerks. And since it is done on a row level, which means that the these analytic functions return the same values for all employees in the same department, we can achieve our goal easily.

MAX function is not the only one analytic function that can be used here. The following example demonstrates the FIRST_VALUE function to achieve the same result:

WITH x AS (
SELECT ename, deptno, job, sal, 
       FIRST_VALUE(DECODE(job,'CLERK',sal)) 
         OVER(ORDER BY DECODE(job,'CLERK',sal) DESC NULLS LAST) max_sal_global,
       FIRST_VALUE(DECODE(job,'CLERK',sal)) 
         OVER(PARTITION BY deptno
              ORDER BY DECODE(job,'CLERK',sal) DESC NULLS LAST) max_sal_dept
FROM scott.emp
)
SELECT ename, deptno, job, sal
FROM x
WHERE max_sal_global=max_sal_dept

As an exercise, try to use LISTAGG analytic function to solve this problem.

Problem #2: Find employees who are paid above the average salary in their respective department.

Again, we will start with a “traditional” approach:

SELECT ename, deptno, job, sal
FROM scott.emp a
WHERE sal > (SELECT AVG(sal)
             FROM scott.emp
             WHERE deptno = a.deptno)
ORDER BY deptno, sal

Result:

ENAME	DEPTNO	JOB	SAL
KING	10	PRESIDENT	5000
JONES	20	MANAGER	2975
SCOTT	20	ANALYST	3000
FORD	20	ANALYST	3000
ALLEN	30	SALESMAN	1600
BLAKE	30	MANAGER	2850

An experienced developer would quickly see that this problem can be solved with the same approach as the problem #1 (above):

WITH x AS (
SELECT ename, deptno, job, sal, AVG(sal) OVER(PARTITION BY deptno) avg_sal
FROM scott.emp
)
SELECT *
FROM x
WHERE sal > avg_sal
ORDER BY deptno, sal

Result:

ENAME	DEPTNO	JOB	SAL	AVG_SAL
KING	10	PRESIDENT	5000	2916.66667
JONES	20	MANAGER	2975	2175
FORD	20	ANALYST	3000	2175
SCOTT	20	ANALYST	3000	2175
ALLEN	30	SALESMAN	1600	1566.66667
BLAKE	30	MANAGER	2850	1566.66667

With this strategy we can even see the department average salary value.

Problem #3: List all employees who work in the same department as the president.

The problem was discussed in one of my old blog posts and I strongly suggest you to check it out: A trick that helps avoiding multiple table scans.

***

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Suggested Reading:

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3 Solutions to 2018 Oracle SQL Puzzle of the Week #14

Yet Another Top Employee Puzzle

Find the employee who remained the top paid employee (excluding the president) the longest period of time between 1980 and 1981

• Use a single SELECT statement only.
• President should be excluded from the analysis.
• Show the number of days the employee remained the top paid person as well as Start Date (hiredate) and End Date (the date when another top employee started)
• The End Date for the last top paid employee in the interval should be 31-DEC-1981.

Expected Result:

EMPNO	ENAME	JOB	SAL	Start Date	End Date	Days on Top
7566	JONES	MANAGER	2975	02-APR-81	03-DEC-81	245

Solutions:

Solution #1. Using RANK to filter the top employee:

WITH x AS ( 
SELECT empno, ename, job, sal, hiredate, 
       MAX(sal)OVER(ORDER BY hiredate) max_sal 
FROM scott.emp  
WHERE job!='PRESIDENT' 
), y AS ( 
SELECT empno, ename, job, sal, hiredate start_date, max_sal,  
       LEAD(hiredate) OVER(ORDER BY hiredate) end_date 
FROM x 
WHERE sal=max_sal 
), z AS ( 
SELECT y.*, LEAST(end_date, date'1981-12-31')-start_date days_on_top, 
RANK()OVER(ORDER BY LEAST(end_date, date'1981-12-31')-start_date DESC) rk 
FROM y 
WHERE EXTRACT(YEAR FROM start_date) IN (1980, 1981)  
) 
SELECT empno,ename,job,sal, start_date "Start Date", 
       end_date "End Date", days_on_top	"Days on Top" 
FROM z 
WHERE rk=1

Solution #2. Using Subquery to filter the top employee:

WITH x AS ( 
SELECT empno, ename, job, sal, hiredate, 
       MAX(sal)OVER(ORDER BY hiredate) max_sal 
FROM scott.emp  
WHERE job!='PRESIDENT' 
  AND hiredate>=date'1980-01-01'  
), y AS ( 
SELECT empno, ename, job, sal, hiredate start_date,  
       LEAST(date'1981-12-31', 
             LEAD(hiredate) OVER(ORDER BY hiredate)) end_date 
FROM x 
WHERE sal=max_sal 
) 
SELECT empno,ename,job,sal, start_date "Start Date", 
       end_date "End Date", end_date-start_date "Days on Top" 
FROM y 
WHERE end_date-start_date=(SELECT MAX(end_date-start_date) FROM y)

Solution #3. Using MODEL with RETURN UPDATED ROWS to filter the top employee:

WITH e AS ( 
SELECT empno, ename, sal, job, LEAST(hiredate, date'1981-12-31') hiredate,  
       MAX(sal)OVER(ORDER BY hiredate) max_sal 
FROM scott.emp 
WHERE hiredate>=date'1980-01-01'  
  AND job!='PRESIDENT' 
), x AS ( 
SELECT empno, ename, job, sal, hiredate,  
       NVL(LEAD(hiredate)OVER(ORDER BY hiredate),
           date'1981-12-31')-hiredate diff, 
       NVL(LEAD(hiredate)OVER(ORDER BY hiredate),
           date'1981-12-31') end_date 
FROM e 
WHERE sal=max_sal 
) 
SELECT empno, ename, job, sal, hiredate "Start Date", 
       end_date "End Date", diff "Days on Top" 
FROM x 
MODEL RETURN UPDATED ROWS 
DIMENSION BY (empno, RANK()OVER(ORDER BY diff DESC) rk) 
MEASURES(ename,job,sal, hiredate, end_date, diff, 0 dummy) 
RULES(dummy[ANY, 1]=1)

The following query will only work as long as there is only 1 top paid employee who stayed on top the longest. In case if we had more than 1 it would only list one of those:

WITH x AS (
SELECT empno, ename, job, sal, hiredate, 
       MAX(sal)OVER(ORDER BY hiredate) max_sal
FROM scott.emp 
WHERE job!='PRESIDENT'
), y AS (
SELECT empno, ename, job, sal, hiredate start_date, 
 LEAST(date'1981-12-31', 
       LEAD(hiredate) OVER(ORDER BY hiredate)) end_date,
 LEAST(date'1981-12-31', 
       LEAD(hiredate) OVER(ORDER BY hiredate))-hiredate days_top
FROM x
WHERE sal=max_sal
ORDER BY days_top DESC NULLS LAST, hiredate
)
SELECT *
FROM y
WHERE ROWNUM=1

You can execute the above SQL statements in Oracle Live SQL environment.
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Further Reading:

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7 Solutions to 2018 Oracle SQL Puzzle of the Week #13

Second Top Employee as of the Start of Employment

List all employees who were 2nd top paid in the entire company as of the time their employment started

• Use a single SELECT statement only.
• At the time of employment start the rank of the employee by salary should be 2.
• Show the top salary at the time when the employee started with the company.
• We assume that no employees have ever been terminated since day 1.

Expected Result:

ENAME	JOB	SAL	HIREDATE	MAX_SAL
WARD	SALESMAN	1250	22-FEB-81	1600
BLAKE	MANAGER	2850	01-MAY-81	2975
FORD	ANALYST	3000	03-DEC-81	5000
SCOTT	ANALYST	3000	19-APR-87	5000

Solutions:

Solution #1. Using LATERAL view, RANK and cumulative MAX analytic functions (Oracle 12g+):

SELECT e.ename, e.job, e.hiredate, e.sal, r.max_sal 
FROM scott.emp e, LATERAL(SELECT a.empno,  
                                 RANK() OVER(ORDER BY a.sal DESC) rk, 
                                 MAX(a.sal) OVER() max_sal 
                          FROM scott.emp a 
                          WHERE a.hiredate<=e.hiredate) r 
WHERE e.empno=r.empno  
  AND rk=2 
ORDER BY e.hiredate

Solution #2. Using CTE, cumulative MAX analytic function and a correlated subquery with COUNT to mimic the filter by RANK:

WITH x AS ( 
SELECT ename, job, hiredate, sal, MAX(sal)OVER(ORDER BY hiredate) max_sal 
FROM scott.emp a 
) 
SELECT * 
FROM x 
WHERE 1=(SELECT COUNT(*) 
         FROM scott.emp 
         WHERE hiredate<=x.hiredate 
           AND sal>x.sal) 
ORDER BY hiredate

Solution #3. Using CTE, cumulative MAX analytic function and an in-line scalar subquery in SELECT to mimic the RANK:

WITH x AS ( 
SELECT ename, job, hiredate, sal, MAX(sal)OVER(ORDER BY hiredate) max_sal, 
       (SELECT COUNT(*)+1 
        FROM scott.emp 
        WHERE sal>e.sal  
          AND hiredate<=e.hiredate) rk 
FROM scott.emp e 
) 
SELECT ename, job, hiredate, sal, max_sal 
FROM x 
WHERE rk=2 
ORDER BY hiredate

Solution #4. Using self-join and Cartesian Product with aggregation:

SELECT a.ename, a.job, a.hiredate, a.sal, MAX(b.sal) max_sal 
FROM scott.emp a JOIN scott.emp b ON b.hiredate<=a.hiredate 
                                 AND b.sal>a.sal 
GROUP BY a.ename, a.job, a.hiredate, a.sal 
HAVING COUNT(DISTINCT b.empno)=1 
ORDER BY a.hiredate

Solution #5. Using CTE and cumulative MAX analytic function (twice):

WITH x AS ( 
SELECT ename, job, hiredate, sal, 
       MAX(sal) OVER(ORDER BY hiredate) max_sal 
FROM scott.emp  
), y  AS ( 
SELECT ename, job, hiredate, sal, max_sal, MAX(sal) OVER(ORDER BY hiredate) max_sal2 
FROM x 
WHERE sal<max_sal 
) 
SELECT ename, job, hiredate, sal, max_sal 
FROM y 
WHERE sal=max_sal2 
ORDER BY hiredate

Solution #6. Using regular and recursive CTEs, ROWNUM, GREATEST, and CASE functions (no Analytic functions!):

WITH e AS ( 
SELECT ename, job, sal, hiredate 
FROM scott.emp 
ORDER BY hiredate 
), x AS ( 
SELECT ename, job, sal, hiredate, ROWNUM rn 
FROM e 
), y(max_sal, sal2, rn) AS ( 
SELECT sal, 0, 1 
FROM x 
WHERE rn=1 
UNION ALL 
SELECT GREATEST(x.sal, y.max_sal) AS max_sal, 
       CASE WHEN x.sal>y.max_sal THEN y.max_sal 
            WHEN x.sal>y.sal2 AND x.sal<=y.max_sal THEN x.sal  
            ELSE y.sal2  
       END AS sal2, 
       x.rn 
FROM x JOIN y ON x.rn=y.rn+1 
) 
SELECT x.ename, x.job, x.sal, x.hiredate, y.max_sal 
FROM y JOIN x ON y.rn=x.rn AND y.sal2=x.sal

Solution #7. Using CTE and MODEL clause to mimic Solution #6:

WITH x AS ( 
SELECT * 
FROM scott.emp 
MODEL 
DIMENSION BY (ROW_NUMBER() OVER(ORDER BY hiredate) rn) 
MEASURES(ename, job, sal, hiredate, sal max_sal, 0 sal2) 
RULES( 
    max_sal[rn>1] = GREATEST(max_sal[CV()-1], sal[CV()]), 
    sal2[rn>1] = CASE WHEN sal[CV()]> max_sal[CV()-1] THEN max_sal[CV()-1] 
                      WHEN sal[CV()]> sal2[CV()-1]   
		       AND sal[CV()]<=max_sal[CV()-1] THEN sal[CV()]  
                      ELSE sal2[CV()-1] 
                 END 
     ) 
) 
SELECT ename, job, sal, hiredate, max_sal 
FROM x 
WHERE sal=sal2

You can execute the above SQL statements in Oracle Live SQL environment.
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Further Reading:

Would you like to read about many more tricks and puzzles?

For more tricks and cool techniques check my book “Oracle SQL Tricks and Workarounds” for instructions.

Interview Question: Get top and bottom paid employees in each department

This is a typical interview problem: list all bottom and top paid employees in each department. A preferred solution should not be using UNION or UNION ALL operators.

Please watch this short video to learn a couple of non-obvious techniques and to impress your potential employers on your next job interview.

My Oracle Group on Facebook:

If you like this post, you may want to join my Oracle group on Facebook: https://www.facebook.com/groups/sqlpatterns/

Would you like to read about many more tricks and puzzles?

For more tricks and cool techniques check my book “Oracle SQL Tricks and Workarounds” for instructions.

 

RANK function and my first video blog post

Hello everyone!

This morning I decided to do my first video blog post. Check it out and provide your feedback and suggestions.

 

My Oracle Group on Facebook:

If you like this post, you may want to join my Oracle group on Facebook: https://www.facebook.com/groups/sqlpatterns/

Would you like to read about many more tricks and puzzles?

For more tricks and cool techniques check my book “Oracle SQL Tricks and Workarounds” for instructions.

3 Solutions to 2018 Oracle SQL Puzzle of the Week #3

2018 Puzzle of the Week #3:

Exact Coin Change Puzzle.

Suppose that you are a sales person at a cash register and you have one purchase to serve before you close. A buyer has to pay X dollars and N cents with bills only (no coins). You have lots of bills of various nomination and limited number of coins: 3 quarters, 9 dimes, 19 nickels, and 4 pennies left in the register. You are required to give the exact change (between 1 and 99 cents) using smallest number of (available) coins.

• Use a single SELECT statement
• The result should return 1 row and 4 columns indicating how many coins of each type to use
• 1 Quarter = 25 cents; 1 Dime = 10 cents; 1 Nickel = 5 cents

Sample result for a change of 63 cents:

 
  Quarters      Dimes    Nickels    Pennies
---------- ---------- ---------- ----------
         2          1          0          3

Solutions:

Solution #1: Using Math formula and MODEL clause:

For American coins one can rely on a mathematical formula to get the smallest number of coins for exact change:

Quarters: FLOOR of [Change Amount]/25
Dimes: FLOOR(([Change Amount] – 25*[Quarters])/10)
Nickels: FLOOR(([Change Amount] – 25*[Quarters]-10*[Dimes])/5)
Pennies: [Change Amount] – 25*[Quarters]-10*[Dimes] – 5*[Nickels]

One of the easiest ways to implement this strategy is to employ the MODEL clause:

WITH m AS (
SELECT 63 AS cents
FROM dual 
)
SELECT cents "Change", 
       Q "Quarters", 
       D "Dimes", 
       N "Nickels", 
       P "Pennies"
FROM m
MODEL
DIMENSION BY(0 AS dummy)
MEASURES(
 cents,
 CAST(0 AS NUMBER(3)) AS Q,
 CAST(0 AS NUMBER(3)) AS D,
 CAST(0 AS NUMBER(3)) AS N,
 CAST(0 AS NUMBER(3)) AS P
)
RULES (
 Q[0]=FLOOR(CENTS[0]/25),
 D[0]=FLOOR((CENTS[0]-Q[0]*25)/10),
 N[0]=FLOOR((CENTS[0]-Q[0]*25-D[0]*10)/5),
 P[0]=(CENTS[0]-Q[0]*25-D[0]*10-N[0]*5)
)

Result:

Change	Quarters	Dimes	Nickels	Pennies
63	2	1	0	3

If we want to extend this solution to see the change combinations for all values from 1 to 99, we will need to change the above solution as follows:

WITH m AS (
SELECT LEVEL cents
FROM dual 
CONNECT BY LEVEL<=99
)
SELECT cents "Change", 
       Q "Quarters", 
       D "Dimes", 
       N "Nickels", 
       P "Pennies"
FROM m
MODEL
PARTITION BY(ROWNUM AS rn)
DIMENSION BY(0 AS dummy)
MEASURES(
 cents,
 CAST(0 AS NUMBER(3)) AS Q,
 CAST(0 AS NUMBER(3)) AS D,
 CAST(0 AS NUMBER(3)) AS N,
 CAST(0 AS NUMBER(3)) AS P
)
RULES (
 Q[0]=FLOOR(CENTS[0]/25),
 D[0]=FLOOR((CENTS[0]-Q[0]*25)/10),
 N[0]=FLOOR((CENTS[0]-Q[0]*25-D[0]*10)/5),
 P[0]=(CENTS[0]-Q[0]*25-D[0]*10-N[0]*5)
)
ORDER BY 1

Result:

Change	Quarters	Dimes	Nickels	Pennies
1	0	0	0	1
2	0	0	0	2
3	0	0	0	3
4	0	0	0	4
5	0	0	1	0
6	0	0	1	1
7	0	0	1	2
8	0	0	1	3
9	0	0	1	4
10	0	1	0	0
…	…	…	…	…
95	3	2	0	0
96	3	2	0	1
97	3	2	0	2
98	3	2	0	3
99	3	2	0	4

Solution #2: Using Enhanced Math formula:

It’s easy to see that the MOD function is very handy in determining the number of coins other than quarters (the largest):

WITH a AS (
SELECT 63 cents
FROM dual
)
SELECT a.cents "Change",
       FLOOR(a.cents/25) "Quarters", 
       FLOOR(MOD(a.cents,25)/10) "Dimes",
       FLOOR(MOD(MOD(a.cents,25),10)/5) "Nickels",
       MOD(MOD(MOD(a.cents,25),10),5) "Pennies"
FROM a

Alternatively, we can see coin combinations for all change amounts from 1 to 99 cents:

WITH a AS (
SELECT LEVEL cents
FROM dual
CONNECT BY LEVEL<100
)
SELECT a.cents "Change",
       FLOOR(a.cents/25) "Quarters", 
       FLOOR(MOD(a.cents,25)/10) "Dimes",
       FLOOR(MOD(MOD(a.cents,25),10)/5) "Nickels",
       MOD(MOD(MOD(a.cents,25),10),5) "Pennies"
FROM a
ORDER BY a.cents

Solution #3: Using Cartesian Product and Top Record pattern approach:

If we did not know the exact math formula, we could still count on the brute force approach – go over all possible coin permutations (Cartesian product) that sum up to the required total amount and then chose the combination with the fewest number of coins (top record pattern):

WITH r AS (
SELECT LEVEL-1 n
FROM dual
CONNECT BY LEVEL<=20
), x AS (
SELECT q.n "Quarters", d.n "Dimes", n.n "Nickels", p.n "Pennies",
 RANK() OVER(ORDER BY q.n + d.n + n.n + p.n) rk
FROM r q, r d, r n, r p
WHERE q.n<=3
 AND d.n<=9
 AND n.n<=19 --not needed
 AND p.n<=4
 AND q.n*25 + d.n*10 + n.n*5 + p.n = 63 --amount of change
)
SELECT "Quarters", "Dimes", "Nickels", "Pennies"
FROM x
WHERE rk=1

If we want to extend this solution to see the change combinations for all values from 1 to 99, we will need to change the above solution as follows:

WITH r AS ( -- this range is to be reused 5 times in this query
SELECT LEVEL-1 n
FROM dual
CONNECT BY LEVEL<=100
), x AS (
SELECT c.n "Change", q.n "Quarters", d.n "Dimes", 
       n.n "Nickels", p.n "Pennies",
       RANK() OVER(PARTITION BY c.n ORDER BY q.n + d.n + n.n + p.n) rk
FROM r q, r d, r n, r p, r c
WHERE q.n<=3
 AND d.n<=9
 AND n.n<=19 --now it is needed
 AND p.n<=4  AND q.n*25 + d.n*10 + n.n*5 + p.n = c.n --amount of change  
 AND c.n>0
)
SELECT "Change", "Quarters", "Dimes", "Nickels", "Pennies"
FROM x
WHERE rk=1
ORDER BY 1

You can execute the above SQL statements in Oracle Live SQL environment.

My Oracle Group on Facebook:

If you like this post, you may want to join my new Oracle group on Facebook: https://www.facebook.com/groups/sqlpatterns/

Would you like to read about many more tricks and puzzles?

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5 Solutions to 2018 Oracle SQL Puzzle of the Week #1

2018 Puzzle of the Week #1:

For a given text string, find the first (from the beginning) longest sub-string that does not have repeating characters.

Solutions:

Solution #1: Using CONNECT BY clause (for range generation), REGEXP_COUNT, and RANK() functions:

WITH w AS ( 
SELECT 'arkansas' AS word 
FROM dual 
), r AS ( 
SELECT ROWNUM rn 
FROM w 
CONNECT BY LEVEL<=LENGTH(word) 
), x AS ( 
SELECT SUBSTR(w.word, r1.rn, r2.rn - r1.rn + 1) substr, 
       RANK() OVER(ORDER BY r2.rn - r1.rn DESC, r1.rn) rk 
FROM r r1, r r2, w 
WHERE r1.rn<=r2.rn 
 AND REGEXP_COUNT(SUBSTR(w.word, r1.rn, r2.rn - r1.rn + 1), '(.).*\1') = 0 
) 
SELECT substr 
FROM x 
WHERE rk=1

Result of execution in Oracle Live SQL client:

SUBSTR
rkans

Solution #2: Using CONNECT BY clause (for range generation), REGEXP_LIKE, and MAX() KEEP functions:

WITH w AS ( 
SELECT 'arkansas' AS word 
FROM dual 
), r AS ( 
SELECT ROWNUM rn 
FROM w 
CONNECT BY LEVEL<=LENGTH(word) 
) 
SELECT MAX(SUBSTR(w.word, r1.rn, r2.rn - r1.rn + 1)) 
 KEEP(DENSE_RANK FIRST ORDER BY r2.rn - r1.rn DESC, r1.rn) substr 
FROM r r1, r r2, w 
WHERE r1.rn<=r2.rn 
 AND NOT REGEXP_LIKE(SUBSTR(w.word, r1.rn, r2.rn - r1.rn + 1), '(.).*\1')

Solution #3: Using CONNECT BY clause (twice), LATERAL view, REGEXP_COUNT, and RANK() functions:

WITH w AS ( 
SELECT 'arkansas' AS word 
FROM dual 
), s AS ( 
SELECT SUBSTR(word, LEVEL) word, LEVEL rn 
FROM w 
CONNECT BY LEVEL<=LENGTH(word) 
) 
SELECT MAX(x.substr) 
       KEEP(DENSE_RANK FIRST ORDER BY LENGTH(x.substr) DESC, s.rn) substr 
FROM s, LATERAL(SELECT SUBSTR(s.word, 1, LEVEL) substr 
                FROM dual 
                CONNECT BY LEVEL<=LENGTH(s.word)) x 
WHERE REGEXP_COUNT(x.substr, '(.).*\1') = 0

Solution #4: Using XMLTable function (for range generation), Correlated subquery with COUNT(DISTINCT), and MAX() KEEP function:

WITH w AS ( 
SELECT 'arkansas' AS word 
FROM dual 
), r AS ( 
SELECT ROWNUM rn, word
FROM w, XMLTABLE('for $i in 1 to $N cast as xs:integer return $i' 
                 PASSING LENGTH(w.word) AS N) x
) 
SELECT MAX(SUBSTR(r1.word, r1.rn, r2.rn - r1.rn + 1))
 KEEP(DENSE_RANK FIRST ORDER BY r2.rn - r1.rn DESC, r1.rn) substr 
FROM r r1, r r2
WHERE r1.rn<=r2.rn 
 AND r2.rn - r1.rn + 1 = 
 (SELECT COUNT(DISTINCT SUBSTR(SUBSTR(r1.word, r1.rn, r2.rn - r1.rn + 1), 
                               LEVEL, 1)) 
 FROM dual 
 CONNECT BY LEVEL<=r2.rn - r1.rn + 1 
 )

Solution #5: Using CONNECT BY, Recursive CTE, INSTR, SUBSTR, and MAX() KEEP functions:

WITH w AS (
 SELECT 'arkansas' word
 FROM dual
), s(sub, word, lvl, rn) AS (
SELECT SUBSTR(word, LEVEL, 1), SUBSTR(word, LEVEL) word, 1, ROWNUM
FROM w
CONNECT BY SUBSTR(word, LEVEL) IS NOT NULL
UNION ALL
SELECT SUBSTR(word, 1, lvl+1), word, lvl+1, ROWNUM
FROM s
WHERE LENGTH(SUBSTR(word, 1, lvl+1))=lvl+1
 AND INSTR(sub, SUBSTR(word, lvl+1, 1))=0
)
SELECT MAX(sub) KEEP (DENSE_RANK FIRST ORDER BY lvl DESC, rn) substr
FROM s

You can execute the above SQL statements in Oracle Live SQL environment.

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Solutions to Puzzle of the Week #8

Puzzle of the Week #8:

Find job titles represented in every department. Write a single SELECT statement only.

Expected Result: (Only clerks and managers work in all 3 departments: 10,20, and 30)

JOB
--------
CLERK
MANAGER

Solutions:

#1: Two COUNT(DISTINCT ..) in HAVING

SELECT job
FROM emp
GROUP BY job
HAVING COUNT(DISTINCT deptno)=(SELECT COUNT(DISTINCT deptno) FROM emp)

#2: Analytic COUNT(DISTINCT ..) with CONNECT BY

SELECT DISTINCT job
FROM (
SELECT job, deptno, LEVEL level#, COUNT(DISTINCT deptno) OVER() cnt
FROM emp
CONNECT BY job=PRIOR job
AND deptno>PRIOR deptno
)
WHERE level#=cnt

#3: Two Analytic COUNT(DISTINCT..)

WITH x AS (
SELECT deptno, job, COUNT(DISTINCT deptno)OVER() cnt, COUNT(DISTINCT deptno)OVER(PARTITION BY job) cnt2
FROM emp
)
SELECT DISTINCT job
FROM x
WHERE cnt=cnt2

OR

WITH x AS (
SELECT deptno, job, COUNT(DISTINCT deptno)OVER() cnt, COUNT(DISTINCT deptno)OVER(PARTITION BY job) cnt2
FROM emp
)
SELECT job
FROM x
WHERE cnt=cnt2
GROUP BY job

#4: Cartesian Product and Two COUNT(DISTINCT ..)

SELECT a.job
FROM emp a, emp b
GROUP BY a.job
HAVING COUNT(DISTINCT a.deptno)=COUNT(DISTINCT b.deptno)

#5: ROLLUP with RANK OVER COUNT(DISTINCT..)

WITH x AS (
SELECT job, COUNT(DISTINCT deptno) cnt, 
       RANK()OVER(ORDER BY COUNT(DISTINCT deptno)  DESC) rk
FROM emp
GROUP BY ROLLUP(job)
)
SELECT job
FROM x
WHERE rk=1
  AND job IS NOT NULL

#6: Analytic COUNT(DITSINCT..) comparison with MINUS

WITH x AS (
SELECT job, 
       CASE WHEN COUNT(DISTINCT deptno)OVER()=COUNT(DISTINCT deptno)OVER(PARTITION BY job) THEN 1 END
FROM emp
MINUS
SELECT job, NULL
FROM emp
)
SELECT job
FROM x

#7: No COUNT(DISTINCT ..) solution:

WITH x AS (
SELECT a.deptno, b.job, NVL(COUNT(c.empno),0) idx
FROM (SELECT DISTINCT deptno FROM emp) a CROSS JOIN (SELECT DISTINCT job FROM emp) b
    LEFT JOIN emp c ON a.deptno=c.deptno AND b.job=c.job
GROUP BY a.deptno, b.job
)
SELECT job
FROM x
GROUP BY job
HAVING MIN(idx)>0

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For more tricks and cool techniques check my book “Oracle SQL Tricks and Workarounds” for instructions.

SQL Puzzle: Find top management in each department – with multiple workaround solutions, by Zahar Hilkevich

I was recently asked by a colleague at work to help him solving a problem that can be interpreted in scott’s emp table terms as the following:

In each department, list all managers and a president, but in the department where the president works, all managers (if any) should be filtered out.

If we look at all managers/president(s), we will see the following result:

ENAME      JOB           DEPTNO
---------- --------- ----------
JONES      MANAGER           20
BLAKE      MANAGER           30
CLARK      MANAGER           10
KING       PRESIDENT         10

Our desired result should exclude CLARK.

Solution/Workaround #1:

SELECT ename, job, deptno
FROM emp a
WHERE job='PRESIDENT'
  OR (job='MANAGER' AND NOT EXISTS(SELECT 1
                                   FROM emp b
                                   WHERE b.deptno=a.deptno
                                     AND job='PRESIDENT')
     )
ORDER BY deptno

Result:
ENAME      JOB           DEPTNO
---------- --------- ----------
KING       PRESIDENT         10
JONES      MANAGER           20
BLAKE      MANAGER           30

This is the most straight-forward solution and it barely requires any explanation.

Workaround #2:

WITH x AS (
SELECT ename, job, deptno, 
       RANK()OVER(PARTITION BY deptno 
                  ORDER BY DECODE(job,'PRESIDENT',1,'MANAGER',2)) rk
FROM emp a
WHERE job IN ('PRESIDENT', 'MANAGER')
)
SELECT ename, job, deptno
FROM x
WHERE rk=1
ORDER BY deptno

Result:
ENAME      JOB           DEPTNO
---------- --------- ----------
KING       PRESIDENT         10
JONES      MANAGER           20
BLAKE      MANAGER           30

Analytical functions make the solution very simple. Here, we use custom sorting (in the ORDER BY) with the RANK function.

Workaround #3:

WITH x AS (
SELECT ename, job, deptno,
       COUNT(DISTINCT job)OVER(PARTITION BY deptno) cnt
FROM emp a
WHERE job IN ('MANAGER', 'PRESIDENT')
)
SELECT ename, job, deptno
FROM x
WHERE job='PRESIDENT' OR cnt=1
ORDER BY deptno

Result:
ENAME      JOB           DEPTNO
---------- --------- ----------
KING       PRESIDENT         10
JONES      MANAGER           20
BLAKE      MANAGER           30

This solution shows a use of COUNT(DISTINCT …)OVER() analytical function.

Workaround #4:

SELECT ename, job, deptno 
FROM emp 
WHERE (deptno, DECODE(job,'PRESIDENT',1,'MANAGER',2)) IN 
  (SELECT deptno, MIN(DECODE(job,'PRESIDENT',1,'MANAGER',2))
   FROM emp
   GROUP BY deptno)
ORDER BY deptno

Result:
ENAME      JOB           DEPTNO
---------- --------- ----------
KING       PRESIDENT         10
JONES      MANAGER           20
BLAKE      MANAGER           30

Another example of the use of custom order hidden in the multi-column subquery.

There are at least 3-5 other workarounds available for this puzzle.

You will have no problems uncovering them after reading my book “Oracle SQL Tricks and Workarounds”.

15 Workarounds for Getting Top Records

To illustrate the concept we will be solving the following problem defined for scott schema:

Find all top paid employees in each department. Display employee names, salaries, jobs, and department.

To qualify for a workaround, a solution’s execution plan should have a distinct hash value (More on that can be found in my book “Oracle SQL Tricks and Workarounds”).

Workaround #1: Correlated subquery

SELECT ename, job, sal, deptno
FROM emp a
WHERE sal=(SELECT MAX(sal)
           FROM emp b
           WHERE b.deptno=a.deptno);

Result:

ENAME      JOB              SAL     DEPTNO
---------- --------- ---------- ----------
BLAKE      MANAGER         2850         30
SCOTT      ANALYST         3000         20
KING       PRESIDENT       5000         10
FORD       ANALYST         3000         20

Execution Plan:

Plan hash value: 1245077725

--------------------------------------------------------------------------------
| Id  | Operation            | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |         |     1 |    47 |     8  (25)| 00:00:01 |
|*  1 |  HASH JOIN           |         |     1 |    47 |     8  (25)| 00:00:01 |
|   2 |   VIEW               | VW_SQ_1 |     3 |    78 |     4  (25)| 00:00:01 |
|   3 |    HASH GROUP BY     |         |     3 |    21 |     4  (25)| 00:00:01 |
|   4 |     TABLE ACCESS FULL| EMP     |    14 |    98 |     3   (0)| 00:00:01 |
|   5 |   TABLE ACCESS FULL  | EMP     |    14 |   294 |     3   (0)| 00:00:01 |
--------------------------------------------------------------------------------

Workaround #2: Correlated subquery with arithmetic transformation

SELECT ename, job, sal, deptno
FROM emp a
WHERE 0=(SELECT MAX(b.sal)-a.sal
         FROM emp b
         WHERE b.deptno=a.deptno)

Execution Plan:

Plan hash value: 2649664444

----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |     1 |    21 |    24   (0)| 00:00:01 |
|*  1 |  FILTER             |      |       |       |            |          |
|   2 |   TABLE ACCESS FULL | EMP  |    14 |   294 |     3   (0)| 00:00:01 |
|   3 |   SORT AGGREGATE    |      |     1 |     7 |            |          |
|*  4 |    TABLE ACCESS FULL| EMP  |     5 |    35 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------

Workaround #3: Non-Correlated subquery

SELECT ename, job, sal, deptno
FROM emp a
WHERE (deptno, sal) IN (SELECT deptno, MAX(sal)
                        FROM emp
                        GROUP BY deptno)

Execution Plan:

Plan hash value: 2491199121

---------------------------------------------------------------------------------
| Id  | Operation            | Name     | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |          |     1 |    47 |     8  (25)| 00:00:01 |
|*  1 |  HASH JOIN SEMI      |          |     1 |    47 |     8  (25)| 00:00:01 |
|   2 |   TABLE ACCESS FULL  | EMP      |    14 |   294 |     3   (0)| 00:00:01 |
|   3 |   VIEW               | VW_NSO_1 |     3 |    78 |     4  (25)| 00:00:01 |
|   4 |    HASH GROUP BY     |          |     3 |    21 |     4  (25)| 00:00:01 |
|   5 |     TABLE ACCESS FULL| EMP      |    14 |    98 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------------

Workaround #4: Aggregating over Cartesian Product

SELECT a.ename, a.job, a.sal, a.deptno
FROM emp a, emp b
WHERE a.deptno=b.deptno
GROUP BY a.ename, a.job, a.sal, a.deptno
HAVING a.sal=MAX(b.sal)

Execution Plan:

Plan hash value: 2435006919

-----------------------------------------------------------------------------
| Id  | Operation            | Name | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |      |     6 |   168 |     8  (25)| 00:00:01 |
|*  1 |  FILTER              |      |       |       |            |          |
|   2 |   HASH GROUP BY      |      |     6 |   168 |     8  (25)| 00:00:01 |
|*  3 |    HASH JOIN         |      |    65 |  1820 |     7  (15)| 00:00:01 |
|   4 |     TABLE ACCESS FULL| EMP  |    14 |   294 |     3   (0)| 00:00:01 |
|   5 |     TABLE ACCESS FULL| EMP  |    14 |    98 |     3   (0)| 00:00:01 |
-----------------------------------------------------------------------------

Workaround #5: Outer Join with IS NULL check

SELECT a.ename, a.job, a.sal, a.deptno
FROM emp a LEFT JOIN emp b ON a.deptno=b.deptno
                          AND a.sal<b.sal
WHERE b.empno IS NULL

Execution Plan:

Plan hash value: 1201587841

----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |     1 |    32 |     7  (15)| 00:00:01 |
|*  1 |  FILTER             |      |       |       |            |          |
|*  2 |   HASH JOIN OUTER   |      |     1 |    32 |     7  (15)| 00:00:01 |
|   3 |    TABLE ACCESS FULL| EMP  |    14 |   294 |     3   (0)| 00:00:01 |
|   4 |    TABLE ACCESS FULL| EMP  |    14 |   154 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------

Workaround #6: Using NOT EXISTS

SELECT ename, job, sal, deptno
FROM emp a
WHERE NOT EXISTS (SELECT 1
                  FROM emp b
                  WHERE b.deptno=a.deptno
                    AND b.sal>a.sal)

Execution Plan:

Plan hash value: 3353202012

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |     5 |   140 |     7  (15)| 00:00:01 |
|*  1 |  HASH JOIN ANTI    |      |     5 |   140 |     7  (15)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP  |    14 |   294 |     3   (0)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| EMP  |    14 |    98 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

Synonymous Workaround for #6 (execution plan has the same hash value): Using COUNT(*)=0 Equivalent

SELECT ename, job, sal, deptno
FROM emp a
WHERE 0=(SELECT COUNT(*)
         FROM emp b
         WHERE b.deptno=a.deptno
           AND b.sal>a.sal)

Execution Plan:

Plan hash value: 3353202012

Workaround #7: Using ALL Predicate

SELECT ename, job, sal, deptno
FROM emp a
WHERE a.sal>=ALL(SELECT b.sal
                 FROM emp b
                 WHERE b.deptno=a.deptno)

Execution Plan:

Plan hash value: 2561671593

---------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |    14 |   294 |    24   (0)| 00:00:01 |
|*  1 |  FILTER            |      |       |       |            |          |
|   2 |   TABLE ACCESS FULL| EMP  |    14 |   294 |     3   (0)| 00:00:01 |
|*  3 |   TABLE ACCESS FULL| EMP  |     2 |    14 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------

Workaround #8: Using In-Line View

SELECT a.ename, a.sal, a.deptno
FROM emp a, (SELECT deptno, MAX(sal) max_sal
             FROM emp
             GROUP BY deptno) b
WHERE a.deptno=b.deptno
  AND a.sal=b.max_sal

Execution Plan:

Plan hash value: 269884559

-----------------------------------------------------------------------------
| Id  | Operation            | Name | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |      |     1 |    39 |     8  (25)| 00:00:01 |
|*  1 |  HASH JOIN           |      |     1 |    39 |     8  (25)| 00:00:01 |
|   2 |   VIEW               |      |     3 |    78 |     4  (25)| 00:00:01 |
|   3 |    HASH GROUP BY     |      |     3 |    21 |     4  (25)| 00:00:01 |
|   4 |     TABLE ACCESS FULL| EMP  |    14 |    98 |     3   (0)| 00:00:01 |
|   5 |   TABLE ACCESS FULL  | EMP  |    14 |   182 |     3   (0)| 00:00:01 |
-----------------------------------------------------------------------------

Workaround #9: Using EXISTS Predicate

SELECT ename, job, sal, deptno
FROM emp a
WHERE EXISTS (SELECT 1
              FROM emp b
              WHERE b.deptno=a.deptno
              HAVING a.sal=MAX(b.sal))

Execution Plan:

Plan hash value: 3057787348

-----------------------------------------------------------------------------
| Id  | Operation            | Name | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |      |     1 |    21 |    24   (0)| 00:00:01 |
|*  1 |  FILTER              |      |       |       |            |          |
|   2 |   TABLE ACCESS FULL  | EMP  |    14 |   294 |     3   (0)| 00:00:01 |
|*  3 |   FILTER             |      |       |       |            |          |
|   4 |    SORT AGGREGATE    |      |     1 |     7 |            |          |
|*  5 |     TABLE ACCESS FULL| EMP  |     5 |    35 |     3   (0)| 00:00:01 |
-----------------------------------------------------------------------------

Synonymous Workaround for #9 (execution plan has the same hash value): Using COUNT(*)>0 Equivalent

SELECT ename, job, sal, deptno
FROM emp a
WHERE 0< (SELECT COUNT(1)
          FROM emp b
          WHERE b.deptno=a.deptno
          HAVING a.sal=MAX(b.sal))

Execution Plan:

Plan hash value: 3057787348

Here is a practical example which happens to qualify as another Synonymous Workaround for #9:

SELECT ename, job, sal, deptno
FROM emp a
WHERE NOT EXISTS (SELECT 1
                  FROM emp b
                  WHERE b.deptno=a.deptno
                  HAVING a.sal<MAX(b.sal))

Execution Plan:

Plan hash value: 3057787348

Workaround #10: Using Analytical Function RANK()

WITH x AS (
SELECT ename, job, sal, deptno,
       RANK()OVER(PARTITION BY deptno ORDER BY sal DESC) rk
FROM emp a
)
SELECT ename, job, sal, deptno
FROM x
WHERE rk=1

Execution Plan:

Plan hash value: 3291446077

---------------------------------------------------------------------------------
| Id  | Operation                | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------
|   0 | SELECT STATEMENT         |      |    14 |   728 |     4  (25)| 00:00:01 |
|*  1 |  VIEW                    |      |    14 |   728 |     4  (25)| 00:00:01 |
|*  2 |   WINDOW SORT PUSHED RANK|      |    14 |   294 |     4  (25)| 00:00:01 |
|   3 |    TABLE ACCESS FULL     | EMP  |    14 |   294 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------------

Workaround #11: Using Analytical Function MAX

WITH x AS (
SELECT ename, job, sal, deptno,
       MAX(sal)OVER(PARTITION BY deptno) max_sal
FROM emp a
)
SELECT ename, job, sal, deptno
FROM x
WHERE sal=max_sal

Execution Plan:

Plan hash value: 4130734685

----------------------------------------------------------------------------
| Id  | Operation           | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |      |    14 |   728 |     4  (25)| 00:00:01 |
|*  1 |  VIEW               |      |    14 |   728 |     4  (25)| 00:00:01 |
|   2 |   WINDOW SORT       |      |    14 |   294 |     4  (25)| 00:00:01 |
|   3 |    TABLE ACCESS FULL| EMP  |    14 |   294 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------

Workaround #12: Using Analytical Function COUNT with CONNECT BY

WITH x AS (
SELECT ename, job, sal, deptno, COUNT(*)OVER(PARTITION BY empno) cnt
FROM emp a
CONNECT BY deptno=PRIOR deptno
       AND sal<PRIOR sal
)
SELECT ename, job, sal, deptno
FROM x
WHERE cnt=1

Execution Plan:

Plan hash value: 704858046

-----------------------------------------------------------------------------------------
| Id  | Operation                      | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |        |    14 |   728 |     2   (0)| 00:00:01 |
|*  1 |  VIEW                          |        |    14 |   728 |     2   (0)| 00:00:01 |
|   2 |   WINDOW SORT                  |        |    14 |   350 |     2   (0)| 00:00:01 |
|*  3 |    CONNECT BY WITHOUT FILTERING|        |       |       |            |          |
|   4 |     TABLE ACCESS BY INDEX ROWID| EMP    |    14 |   350 |     2   (0)| 00:00:01 |
|   5 |      INDEX FULL SCAN           | PK_EMP |    14 |       |     1   (0)| 00:00:01 |
-----------------------------------------------------------------------------------------

Workaround #13: Using Analytical Function COUNT with CONNECT BY filtered by LEVEL

WITH x AS (
SELECT ename, job, sal, deptno, COUNT(*)OVER(PARTITION BY empno) cnt
FROM emp a
WHERE level<=2
CONNECT BY deptno=PRIOR deptno
       AND sal<PRIOR sal
)
SELECT ename, job, sal, deptno
FROM x
WHERE cnt=1

Execution Plan:

Plan hash value: 2668428643

------------------------------------------------------------------------------------------
| Id  | Operation                       | Name   | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                |        |    14 |   728 |     2   (0)| 00:00:01 |
|*  1 |  VIEW                           |        |    14 |   728 |     2   (0)| 00:00:01 |
|   2 |   WINDOW SORT                   |        |    14 |   350 |     2   (0)| 00:00:01 |
|*  3 |    FILTER                       |        |       |       |            |          |
|*  4 |     CONNECT BY WITHOUT FILTERING|        |       |       |            |          |
|   5 |      TABLE ACCESS BY INDEX ROWID| EMP    |    14 |   350 |     2   (0)| 00:00:01 |
|   6 |       INDEX FULL SCAN           | PK_EMP |    14 |       |     1   (0)| 00:00:01 |
------------------------------------------------------------------------------------------

Workaround #14: CONNECT BY with GROUP BY and HAVING

SELECT ename, job, sal, deptno
FROM emp a
CONNECT BY deptno=PRIOR deptno
       AND sal<PRIOR sal
GROUP BY ename, job, sal, deptno
HAVING COUNT(*)=1

Execution Plan:

Plan hash value: 2144516570

---------------------------------------------------------------------------------------
| Id  | Operation                      | Name | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |      |     1 |    21 |     4  (25)| 00:00:01 |
|*  1 |  FILTER                        |      |       |       |            |          |
|   2 |   HASH GROUP BY                |      |     1 |    21 |     4  (25)| 00:00:01 |
|*  3 |    CONNECT BY WITHOUT FILTERING|      |       |       |            |          |
|   4 |     TABLE ACCESS FULL          | EMP  |    14 |   294 |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------------------

Workaround #15: GROUP BY and HAVING over CONNECT BY filtered by LEVEL

SELECT ename, job, sal, deptno
FROM emp a
WHERE level<=2
CONNECT BY deptno=PRIOR deptno
       AND sal<PRIOR sal
GROUP BY ename, job, sal, deptno
HAVING COUNT(*)=1

Execution Plan:

Plan hash value: 1946770371

----------------------------------------------------------------------------------------
| Id  | Operation                       | Name | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                |      |     1 |    21 |     4  (25)| 00:00:01 |
|*  1 |  FILTER                         |      |       |       |            |          |
|   2 |   HASH GROUP BY                 |      |     1 |    21 |     4  (25)| 00:00:01 |
|*  3 |    FILTER                       |      |       |       |            |          |
|*  4 |     CONNECT BY WITHOUT FILTERING|      |       |       |            |          |
|   5 |      TABLE ACCESS FULL          | EMP  |    14 |   294 |     3   (0)| 00:00:01 |
----------------------------------------------------------------------------------------

If you want to learn how to come up with numerous workarounds on your own, check my book “Oracle SQL Tricks and Workarounds” for instructions.