--列轉行（資料對稱型）

--需求：將test的資料轉換為如下所示：

drop table test;
CREATE TABLE TEST (
YEARS NUMBER,
Q NUMBER,
AMT NUMBER
);

INSERT INTO TEST(YEARS,Q,AMT) VALUES(2020,1,2000);
INSERT INTO TEST(YEARS,Q,AMT) VALUES(2020,2,3500);
INSERT INTO TEST(YEARS,Q,AMT) VALUES(2020,3,4000);
INSERT INTO TEST(YEARS,Q,AMT) VALUES(2020,4,5000);
INSERT
 
 INTO TEST(YEARS,Q,AMT) VALUES(2021,1,1500);
INSERT INTO TEST(YEARS,Q,AMT) VALUES(2021,2,3000);
INSERT INTO TEST(YEARS,Q,AMT) VALUES(2021,3,4000);
INSERT INTO TEST(YEARS,Q,AMT) VALUES(2021,4,5000);
COMMIT;

--方法一：使用LEAD函式(只適用於資料對稱的列轉行)

SELECT YEARS AS YEAR,
       AMT Q1,
       L1 Q2,
       L2 Q3,
       L3 Q4
 
FROM (SELECT T.*,
                   LEAD(AMT,1) OVER(PARTITION BY YEARS ORDER BY Q) L1,
                   LEAD(AMT,2) OVER(PARTITION BY YEARS ORDER BY Q) L2,
                   LEAD(AMT,3) OVER(PARTITION BY YEARS ORDER BY Q) L3
            FROM TEST T) A
WHERE Q=1;

--方法二：使用LAG函式(只適用於資料對稱的列轉行)

SELECT
 
 YEARS AS YEAR,
       L3 Q1,
       L2 Q2,
       L1 Q3,
       AMT Q4
FROM (SELECT T.*,
                 LAG(AMT,1) OVER(PARTITION BY YEARS ORDER BY Q) L1,
                 LAG(AMT,2) OVER(PARTITION BY YEARS ORDER BY Q) L2,
                 LAG(AMT,3) OVER(PARTITION BY YEARS ORDER BY Q) L3
          FROM TEST T) A
WHERE Q=4;

--方法三：使用CASE WHEN函式（適用於所有情況的列轉行）

SELECT YEARS AS YEAR,
       SUM(CASE WHEN Q=1 THEN AMT ELSE NULL END) AS Q1,
       SUM(CASE WHEN Q=2 THEN AMT ELSE NULL END) AS Q2,
       SUM(CASE WHEN Q=3 THEN AMT ELSE NULL END) AS Q3,
       SUM(CASE WHEN Q=4 THEN AMT ELSE NULL END) AS Q4
FROM TEST
GROUP BY YEARS;

--方法四：使用DECODE函式（在Oracle中適用於所有情況的列轉行）

SELECT YEARS AS YEAR,
       MAX(DECODE(Q,1,AMT)) Q1,
       MAX(DECODE(Q,2,AMT)) Q2,
       MAX(DECODE(Q,3,AMT)) Q3,
       MAX(DECODE(Q,4,AMT)) Q4
FROM TEST
GROUP BY YEARS;

--方法五：使用自關聯(只適用於資料對稱的列轉行)

SELECT A.YEARS AS YEAR,
       A.AMT AS Q1,
       B.AMT AS Q2,
       C.AMT AS Q3,
       D.AMT AS Q4
FROM (SELECT * FROM TEST WHERE Q=1) A
  JOIN (SELECT * FROM TEST WHERE Q=2) B
    ON A.YEARS=B.YEARS
  JOIN (SELECT * FROM TEST WHERE Q=3) C
    ON A.YEARS=C.YEARS
  JOIN (SELECT * FROM TEST WHERE Q=4) D
    ON A.YEARS=D.YEARS;

--方法六：使用pivot

select *
from test
pivot
(max(amt) for Q in ('1' as Q1 ,'2' as Q2,'3' as Q3,'4' as Q4));

-------行轉列，使用unpivot

SELECT YEARS,Q,AMT
FROM TEST1
UNPIVOT
(AMT FOR Q in (Q1,Q2,Q3,Q4));