Three Soluitions to Puzzle of the Week #17

Puzzle of the Week #17:

Write a single SELECT statement that would show the years of hire in each department. The result should have 3 columns (see below): deptno, year1, and year2. If a department only hired during 1 calendar year, this year should be shown in year1 column (see deptno 30) and year2 column should be blank. If a department hired during 2 calendar years, the first year should be should be shown in year1 column, and the 2nd year should be shown in year2 column (see deptno 10). In all other cases, show 1st year in year1 column and “More (N)” where N is the number of years that department did the hiring (see deptno 20).

Expected Result:

DEPTNO Year 1   Year 2
------ -------- --------
    10 1981     1982
    20 1980     More (3)
    30 1981

Solutions

#1: Using COUNT(DISTINCT ..)

SELECT deptno, MIN(EXTRACT(YEAR FROM hiredate)) AS "Year 1",
       CASE COUNT(DISTINCT EXTRACT(YEAR FROM hiredate))
            WHEN 1 THEN ''
            WHEN 2 THEN TO_CHAR(MAX(EXTRACT(YEAR FROM hiredate)))
            ELSE 'More (' || COUNT(DISTINCT EXTRACT(YEAR FROM hiredate)) || ')'
       END AS "Year 2"
FROM emp
GROUP BY deptno
ORDER BY 1;

DEPTNO     Year 1 Year 2
------ ---------- --------
    10       1981 1982
    20       1980 More (3)
    30       1981

#2: Using DENSE_RANK Analytic Function

WITH x AS (
SELECT deptno, EXTRACT(YEAR FROM hiredate) hire_year,
       DENSE_RANK()OVER(PARTITION BY deptno ORDER BY EXTRACT(YEAR FROM hiredate)) rk
FROM emp
)
SELECT deptno, MIN(hire_year) "Year 1",
       CASE MAX(rk) WHEN 1 THEN ''
                    WHEN 2 THEN CAST(MAX(hire_year) AS CHAR(4))
                    ELSE 'More (' || MAX(rk) || ')'
       END AS "Year 2"
FROM x
GROUP BY deptno
ORDER BY 1;

DEPTNO     Year 1 Year 2
------ ---------- --------
    10       1981 1982
    20       1980 More (3)
    30       1981

#3: Using PIVOT clause

SELECT deptno, Y1 "Year 1",
       CASE WHEN cnt>2 THEN 'More (' || cnt || ')'
       ELSE TO_CHAR(Y2)
       END "Year 2"
FROM
(
SELECT deptno, EXTRACT(YEAR FROM hiredate) yr,
       CASE DENSE_RANK()OVER(PARTITION BY deptno ORDER BY EXTRACT(YEAR FROM hiredate))
       WHEN 1 THEN 'Y1'
            WHEN 2 THEN 'Y2'
       END AS Y,
       COUNT(DISTINCT EXTRACT(YEAR FROM hiredate))OVER(PARTITION BY deptno) cnt
FROM emp
)
PIVOT
(
  MAX(yr)
  FOR y IN ('Y1' y1,'Y2' y2)
);

DEPTNO     Year 1 Year 2
------ ---------- --------
    10       1981 1982
    20       1980 More (3)
    30       1981

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?

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

 

 

 

 

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s