convert column to row in oracle [duplicate] - sql

Question

This question already has answers here:
Using pivot on multiple columns of an Oracle row
(3 answers)
Closed 10 months ago.
I have a question, is there any method that convert colum to row.
for example,I have a table like this:
CREATE TABLE mytable(u_id, month, offer, revenue) as
SELECT 1, 'January', 'Offer_1', 45 FROM dual
UNION ALL
SELECT 1, 'February','Offer_2', 40 FROM dual
UNION ALL
SELECT 1, 'March' ,'Offer_1', 35 FROM dual
UNION ALL
SELECT 2, 'January' ,'Offer_2', 40 FROM dual
UNION ALL
SELECT 2, 'February','Offer_3', 40 FROM dual
UNION ALL
SELECT 2, 'March' ,'Offer_1', 50 FROM dual;
and my expected table is
(There should be one row per user)
u_id
january_offer
january_revenue
february_offer
february_revenue
march_offer
march_revenue
1
Offer_1
45
Offer_2
40
Offer_1
35
2
Offer_2
40
Offer_3
40
Offer_1
50
I tried:
SELECT t1.u_id,
t1.january_offer,
t1.january_revenue,
t2.february_offer,
t2.february_revenue,
t3.march_offer,
t3.march_revenue
FROM (SELECT u_id, offer AS january_offer,
revenue AS january_revenue
FROM mytable
WHERE month = 'January') t1
LEFT JOIN (SELECT u_id,
offer AS february_offer,
revenue AS february_revenue
FROM mytable t1
WHERE month = 'February') t2
ON t1.u_id = t2.u_id
LEFT JOIN (SELECT u_id, offer AS march_offer,
revenue AS march_revenue
FROM mytable t1
WHERE month = 'March') t3
ON t2.u_id = t3.u_id
but,real, I have lots of data and a long SQL script and this method aggravates my script.

Answer 1

This is what PIVOT is designed for:
SELECT *
FROM package
PIVOT (
MAX(offer) AS offer, MAX(revenue) AS revenue
FOR month IN ( 'January' AS january, 'February' AS feburary, 'March' AS march )
)
Which, for the sample data:
CREATE TABLE package (U_id, month, offer,revenue) AS
SELECT 1, 'January', 'offer_1', 45 FROM DUAL UNION ALL
SELECT 1, 'February', 'offer_2', 40 FROM DUAL UNION ALL
SELECT 1, 'March', 'offer_1', 35 FROM DUAL UNION ALL
SELECT 2, 'January', 'offer_2', 40 FROM DUAL UNION ALL
SELECT 2, 'February', 'offer_3', 40 FROM DUAL UNION ALL
SELECT 2, 'March', 'offer_1', 50 FROM DUAL;
Outputs:
U_ID
JANUARY_OFFER
JANUARY_REVENUE
FEBURARY_OFFER
FEBURARY_REVENUE
MARCH_OFFER
MARCH_REVENUE
1
offer_1
45
offer_2
40
offer_1
35
2
offer_2
40
offer_3
40
offer_1
50
db<>fiddle here

Answer 2

An alternative pattern that might be more efficient is to use a case expression:
SELECT t1.u_id
, CASE month WHEN 'January' then offer END AS january_offer
, CASE month WHEN 'January' then revenue END AS january_revenue
, CASE month WHEN 'February' then offer END AS february_offer
, ...
From there you can use an aggregate function to eliminate null rows:
SELECT u_id
, MAX(january_offer) AS january_offer
, MAX(january_revenue) AS january_revenue
, MAX(february_offer) AS february_offer
, ...
FROM (
SELECT t1.u_id
, CASE month WHEN 'January' then offer END AS january_offer
, CASE month WHEN 'February' then offer END AS february_offer
, ...
) AS t
GROUP BY u_id
In general, this kind of operation is better handled in the presentation layer of the application than in the database layer.

Answer 3

You can use conditional aggregation along with CASE..WHEN expressions such as
SELECT u_id,
MAX(CASE WHEN month = 'January' THEN offer END) AS january_offer,
MAX(CASE WHEN month = 'January' THEN revenue END) AS january_revenue,
MAX(CASE WHEN month = 'February' THEN offer END) AS february_offer,
MAX(CASE WHEN month = 'February' THEN revenue END) AS february_revenue,
MAX(CASE WHEN month = 'March' THEN offer END) AS march_offer,
MAX(CASE WHEN month = 'March' THEN revenue END) AS march_revenue
FROM t
GROUP BY u_id
or by using DECODE() function such as
SELECT u_id,
MAX(DECODE (month , 'January', offer)) AS january_offer,
MAX(DECODE (month , 'January', revenue)) AS january_revenue,
MAX(DECODE (month , 'February', offer)) AS february_offer,
MAX(DECODE (month , 'February', revenue)) AS february_revenue,
MAX(DECODE (month , 'March', offer)) AS march_offer,
MAX(DECODE (month , 'March', revenue)) AS march_revenue
FROM t
GROUP BY u_id
Demo