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
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