oracle row to column, column to row summary

1. Row to Column

(1) decode implementation

SELECT t_year,
MAX(DECODE(t_month,'January',t_value)) AS January,
MAX(DECODE(t_month,'February',t_value)) AS February,
MAX(DECODE(t_month,'March',t_value)) AS March,
MAX(DECODE(t_month,'April',t_value)) AS April
FROM a_testtable WHERE t_month IN('1month','February','March','April')
GROUP BY t_year;

(2) case when implementation

SELECT t_year,
MAX(CASE t_month WHEN 'January' THEN t_value END) AS January,
MAX(CASE t_month WHEN 'February' THEN t_value END) AS February,
MAX(CASE t_month WHEN 'March' THEN t_value END) AS March,
MAX(CASE t_month WHEN 'April' THEN t_value END) AS April
FROM a_testtable WHERE t_month IN('January','February','March','April')
GROUP BY t_year;

(3) pivot function

SELECT * FROM a_testtable
PIVOT(SUM(t_value) FOR t_month IN('January' AS January,'February' AS February,'March' AS March,'April' AS Fourmonth));

SELECT * FROM
(SELECT t_year AS ye,t_month AS mon,t_value AS val FROM a_testtable) a
PIVOT(SUM(val) FOR mon IN('January' AS January,'February' AS February, 'March' AS March, 'April' AS April));

2-column line change

Prepare tables and data

(1) decode implementation

SELECT t_year,
DECODE(lvl,1,'January',2,'February',3,'March',4,'April') AS t_month,
DECODE(lvl,1,one_m,2,two_m,3,tree_m,4,four_m) AS t_qty
FROM b_testtable,(SELECT LEVEL lvl FROM dual CONNECT BY LEVEL<=4)
ORDER BY t_year,t_month;

(2) case when implementation

SELECT t_year,
CASE lvl WHEN 1 THEN 'January'
WHEN 2 THEN 'February'
WHEN 3 THEN 'March'
WHEN 4 THEN 'April'
END AS t_month,
CASE lvl WHEN 1 THEN one_m
WHEN 2 THEN two_m
WHEN 3 THEN tree_m
WHEN 4 THEN four_m
END AS t_qty
FROM b_testtable,(SELECT LEVELlvl FROM dual CONNECT BY LEVEL<=4)
ORDER BY t_year,t_month;

(3) Unpivot function implementation

SELECT * FROM b_testtable
UNPIVOT(t_qty FOR t_month IN(one_m AS 'January',two_m AS 'February',tree_m AS 'March',four_m AS 'April'))
ORDERBY t_year,t_month;