9 Solutions to Puzzle of the Week #21

Puzzle of the Week #21:

Produce a report that shows employee name, his/her immediate manager name, and the next level manager name. The following conditions should be met:

  • Use Single SELECT statement only
  • Use mgr column to identify employee’s immediate manager
  • The query should work in Oracle 11g.
  • A preferred solution should use only a single instance of emp table.

Expected Result:

NAME1      NAME2      NAME3
---------- ---------- ------
SMITH      FORD       JONES
ALLEN      BLAKE      KING
WARD       BLAKE      KING
JONES      KING
MARTIN     BLAKE      KING
BLAKE      KING
CLARK      KING
SCOTT      JONES      KING
KING
TURNER     BLAKE      KING
ADAMS      SCOTT      JONES
JAMES      BLAKE      KING
FORD       JONES      KING
MILLER     CLARK      KING

Solutions:

#1. Using connect_by_root, sys_connect_by_path, and regexp_substr functions

col name1 for a10
col name2 for a10
col name3 for a10
WITH x AS(
SELECT CONNECT_BY_ROOT(ename) name,
       SYS_CONNECT_BY_PATH(ename, ',') path,
       CONNECT_BY_ROOT(empno) empno
FROM emp
WHERE LEVEL<=3
CONNECT BY empno=PRIOR mgr
)
SELECT name, REGEXP_SUBSTR(MAX(path), '[^,]+', 1, 2) name2,
             REGEXP_SUBSTR(MAX(path), '[^,]+', 1, 3) name3
FROM x
GROUP BY name, empno
ORDER BY empno;

#2. Using CONNECT BY twice

WITH x AS (
SELECT ename, PRIOR ename mname, empno, mgr
FROM emp
WHERE LEVEL=2 OR mgr IS NULL
CONNECT BY PRIOR empno=mgr
)
SELECT ename name1, mname name2, MAX(PRIOR mname) name3
FROM x
WHERE LEVEL<=2
CONNECT BY PRIOR empno=mgr
GROUP BY ename, mname, empno
ORDER BY empno

#3. Using CONNECT BY and Self Outer Join

WITH x AS (
SELECT ename, PRIOR ename mname, PRIOR mgr AS mgr, empno
FROM emp
WHERE LEVEL=2 OR mgr IS NULL
CONNECT BY PRIOR empno=mgr
)
SELECT x.ename name1, x.mname name2, e.ename name3
FROM x LEFT JOIN emp e ON x.mgr=e.empno
ORDER BY x.empno

#4. Using 2 Self Outer Joins

SELECT a.ename name1, b.ename name2, c.ename name3
FROM emp a LEFT JOIN emp b ON a.mgr=b.empno
           LEFT JOIN emp c ON b.mgr=c.empno
ORDER BY a.empno

#5. Using CONNECT BY and PIVOT

SELECT name1, name2, name3
FROM (
SELECT ename, LEVEL lvl, CONNECT_BY_ROOT(empno) empno
FROM emp
WHERE LEVEL<=3
CONNECT BY empno=PRIOR mgr
)
PIVOT(
MAX(ename)
FOR lvl IN (1 AS name1, 2 AS name2, 3 AS name3)
)
ORDER BY empno;

#6. PIVOT Simulation

WITH x AS (
SELECT ename, LEVEL lvl, CONNECT_BY_ROOT(empno) empno
FROM emp
WHERE LEVEL<=3
CONNECT BY empno=PRIOR mgr
)
SELECT MAX(DECODE(lvl, 1, ename)) name1,
       MAX(DECODE(lvl, 2, ename)) name2,
       MAX(DECODE(lvl, 3, ename)) name3
FROM x
GROUP BY empno
ORDER BY empno;

#7. Using CONNECT BY and no WITH/Subqueries (Credit to Krishna Jamal)

SELECT ename Name1, PRIOR ename Name2,
DECODE(LEVEL, 
    3, CONNECT_BY_ROOT(ename), 
    4, TRIM(BOTH ' ' FROM 
        REPLACE(
            REPLACE(SYS_CONNECT_BY_PATH(PRIOR ename, ' '), PRIOR ename), 
        CONNECT_BY_ROOT(ename)))
        ) Name3
FROM emp
START WITH mgr IS NULL
CONNECT BY PRIOR empno = mgr
ORDER BY empno;

#8. A composition of Methods 1 and 7:

SELECT ename Name1, PRIOR ename Name2,
       CASE WHEN LEVEL IN (3,4) 
          THEN REGEXP_SUBSTR(SYS_CONNECT_BY_PATH(ename, ','),'[^,]+',1,LEVEL-2) 
       END AS Name3
FROM emp
START WITH mgr IS NULL
CONNECT BY PRIOR empno = mgr
ORDER BY empno;

#9. Using NTH_VALUE Analytic function (Oracle 11.2 and up):

WITH x AS (
SELECT CONNECT_BY_ROOT(ename) n1, CONNECT_BY_ROOT(empno) empno,
 NTH_VALUE(ename, 2) OVER(PARTITION BY CONNECT_BY_ROOT(ename) ORDER BY LEVEL) n2,
 NTH_VALUE(ename, 3) OVER(PARTITION BY CONNECT_BY_ROOT(ename) ORDER BY LEVEL) n3
FROM emp
WHERE LEVEL<=3
CONNECT BY empno=PRIOR mgr
)
SELECT n1 name1, MAX(n2) name2, MAX(n3) name3
FROM x
GROUP BY n1, empno
ORDER BY empno

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Puzzle of the Week Challenge – Solutions to the 1st Puzzle

Last week we started a new contest, Puzzle of the Week. Today we publish correct answers for the 1st puzzle:

jigsaw-puzzle-piece Write a single SELECT statement that would output a calendar for the current month in a traditional tabular format (7 columns: Sun-Sat).

 

Solution #1: No Sub-query solution! We consider it the best solution.

To better understand the following query we suggest you to first check if you can understand Solution #3 (see below).

SELECT MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'), 
                  '1', LEVEL)) SUN,
       MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'),
                  '2', LEVEL)) MON,
       MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'), 
                  '3', LEVEL)) TUE,
       MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'), 
                  '4', LEVEL)) WED,
       MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'), 
                  '5', LEVEL)) THU,
       MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'), 
                  '6', LEVEL)) FRI,
       MIN(DECODE (TO_CHAR (TRUNC(SYSDATE,'MON') + LEVEL - 1, 'd'), 
                  '7', LEVEL)) SAT
FROM DUAL
CONNECT BY LEVEL <= TO_CHAR(LAST_DAY(SYSDATE),'DD')
GROUP BY TRUNC(TRUNC(SYSDATE,'MON') + LEVEL-1, 'DAY')
ORDER BY TRUNC(TRUNC(SYSDATE,'MON') + LEVEL-1, 'DAY');

 

Solution #2: Using PIVOT

SELECT "'SUN'" SU,"'MON'" MO,"'TUE'" TU,"'WED'" WE,
       "'THU'" TH,"'FRI'" FR,"'SAT'" SA
FROM
(
  SELECT TRUNC(TRUNC(SYSDATE,'MON')+LEVEL-1,'DAY') WEEK_START,  
         TO_CHAR(TRUNC(SYSDATE,'MON')+LEVEL-1,'DD') DD, 
         TO_CHAR(TRUNC(SYSDATE,'MON')+LEVEL-1,'DY') DY  
  FROM DUAL
  CONNECT BY TO_CHAR(TRUNC(SYSDATE,'MON')+LEVEL-1,'yyyymm')=
             TO_CHAR(SYSDATE,'yyyymm')
)
PIVOT 
(
  MAX(DD)
  FOR DY IN ('SUN','MON','TUE','WED','THU','FRI','SAT')
)
ORDER BY week_start;

 

Solution #3: Use the power of CONNECT BY clause to generate a range of days for the current month

WITH x AS (
SELECT TRUNC(SYSDATE, 'MON')+level-1 d
FROM DUAL
CONNECT BY MONTHS_BETWEEN(TRUNC(SYSDATE, 'MON')+level-1, TRUNC(SYSDATE, 'MON'))<1
)
SELECT MAX(CASE WHEN TO_CHAR(D,'DY')='SUN' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS SUN,
       MAX(CASE WHEN TO_CHAR(D,'DY')='MON' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS MON,
       MAX(CASE WHEN TO_CHAR(D,'DY')='TUE' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS TUE,
       MAX(CASE WHEN TO_CHAR(D,'DY')='WED' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS WED,
       MAX(CASE WHEN TO_CHAR(D,'DY')='THU' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS THU,
       MAX(CASE WHEN TO_CHAR(D,'DY')='FRI' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS FRI,
       MAX(CASE WHEN TO_CHAR(D,'DY')='SAT' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS SAT
FROM X
GROUP BY TRUNC(D, 'DAY')
ORDER BY TRUNC(D, 'DAY')

Solution #4: Use existing table(s) to generate a range of days for the current month

WITH X AS (
SELECT TRUNC(SYSDATE, 'MON')+ROWNUM-1 D
FROM emp,emp 
WHERE TO_CHAR(TRUNC(SYSDATE, 'MON')+ROWNUM-1, 'YYYYMM')=TO_CHAR(SYSDATE, 'YYYYMM')
  AND ROWNUM<=31
)
SELECT MAX(CASE WHEN TO_CHAR(D,'DY')='SUN' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS SUN,
       MAX(CASE WHEN TO_CHAR(D,'DY')='MON' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS MON,
       MAX(CASE WHEN TO_CHAR(D,'DY')='TUE' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS TUE,
       MAX(CASE WHEN TO_CHAR(D,'DY')='WED' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS WED,
       MAX(CASE WHEN TO_CHAR(D,'DY')='THU' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS THU,
       MAX(CASE WHEN TO_CHAR(D,'DY')='FRI' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS FRI,
       MAX(CASE WHEN TO_CHAR(D,'DY')='SAT' THEN TO_CHAR(D,'DD') 
                ELSE '  ' END) AS SAT
FROM X
GROUP BY TRUNC(D, 'DAY')
ORDER BY TRUNC(D, 'DAY')

 

Solution #5: Present each calendar week as a single column value – using LISTAGG function

WITH X AS (
SELECT TRUNC(SYSDATE, 'MON')+level-1 d
FROM DUAL
CONNECT BY MONTHS_BETWEEN(TRUNC(SYSDATE, 'MON')+LEVEL-1, TRUNC(SYSDATE, 'MON'))<1
), y AS (
SELECT LISTAGG(TO_CHAR(d,'DD'), '  ') WITHIN GROUP(ORDER BY d) AS week, TRUNC(D, 'DAY') wday
FROM X
GROUP BY TRUNC(D, 'DAY')
)
SELECT CASE WHEN week LIKE '01%' THEN LPAD(week, 26)
            ELSE week
       END AS "SUN MON TUE WED THU FRI SAT"
FROM y
ORDER BY wday

 

Solution #6: Present each calendar week as a single column value – using SYS_CONNECT_BY_PATH function

WITH X AS (
SELECT TRUNC(SYSDATE, 'MON')+level-1 d
FROM DUAL
CONNECT BY MONTHS_BETWEEN(TRUNC(SYSDATE, 'MON')+LEVEL-1, TRUNC(SYSDATE, 'MON'))<1
)
SELECT CASE WHEN MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' ')) LIKE ' 01%' THEN
                LPAD(MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' ')), 21)
            ELSE MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' '))
       END " SU MO TU WE TH FR SA"
FROM x
CONNECT BY d=PRIOR d+1 AND TRUNC(d,'DAY')=TRUNC(PRIOR d, 'DAY')
START WITH TO_CHAR(d,'DD')='01' OR d=TRUNC(d,'DAY')
GROUP BY TRUNC(d, 'DAY')
ORDER BY 1

 

Solution #7: A variation of Solution #6

SELECT CASE 
       WHEN MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' ')) LIKE ' 01%' THEN
                LPAD(MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' ')), 21)
            ELSE MAX(SYS_CONNECT_BY_PATH(TO_CHAR(d, 'DD'), ' '))
       END " SU MO TU WE TH FR SA"
FROM (SELECT TRUNC(SYSDATE, 'MON')+level-1 d
      FROM DUAL
      CONNECT BY MONTHS_BETWEEN(TRUNC(SYSDATE, 'MON')+LEVEL-1, TRUNC(SYSDATE, 'MON'))<1) x
CONNECT BY d=PRIOR d+1 AND TRUNC(d,'DAY')=TRUNC(PRIOR d, 'DAY')
START WITH TO_CHAR(d,'DD')='01' OR d=TRUNC(d,'DAY')
GROUP BY TRUNC(d, 'DAY')
ORDER BY 1

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