How to convert column into rows in oracle 10g - sql

Question

Suppose I have the result of an Oracle sql query:
Month Date
----- -----
Jan 10
Jan 15
Jan 20
Feb 11
Feb 16
Feb 25
I want to display this data in the following format:
Jan Jan Jan Feb Feb Feb
10 15 20 11 16 25
How to write the query?

Answer 1

Using PIVOT:
SQL> WITH sample_data AS(
2 SELECT 'Jan' mnth, 10 dt FROM dual UNION ALL
3 SELECT 'Jan' mnth, 15 dt FROM dual UNION ALL
4 SELECT 'Jan' mnth, 20 dt FROM dual UNION ALL
5 SELECT 'Feb' mnth, 11 dt FROM dual UNION ALL
6 SELECT 'Feb' mnth, 16 dt FROM dual UNION ALL
7 SELECT 'Feb' mnth, 25 dt FROM dual
8 )
9 -- end of smaple_data mimicking real table
10 SELECT *
11 FROM
12 (SELECT dt, row_number() OVER(ORDER BY NULL) rn FROM sample_data
13 ) PIVOT (MAX(dt) FOR (rn)
14 IN (1 AS Jan_1, 2 AS jan_2, 3 AS Jan_3, 4 AS Feb_1, 5 Feb_2, 6 Feb_3));
JAN_1 JAN_2 JAN_3 FEB_1 FEB_2 FEB_3
---------- ---------- ---------- ---------- ---------- ----------
10 15 20 11 16 25
Under the hood PIVOT is same MAX + CASE. You can check it in 12c where Oracle added EXPAND_SQL_TEXT procedure to DBMS_UTILITY package.
SQL> VARIABLE c CLOB
SQL> BEGIN
2 dbms_utility.expand_sql_text(Q'[WITH sample_data AS(
3 SELECT 'Jan' mnth, 10 dt FROM dual UNION ALL
4 SELECT 'Jan' mnth, 15 dt FROM dual UNION ALL
5 SELECT 'Jan' mnth, 20 dt FROM dual UNION ALL
6 SELECT 'Feb' mnth, 11 dt FROM dual UNION ALL
7 SELECT 'Feb' mnth, 16 dt FROM dual UNION ALL
8 SELECT 'Feb' mnth, 25 dt FROM dual
9 )
10 -- end of smaple_data mimicking real table
11 SELECT *
12 FROM
13 (SELECT dt, row_number() OVER(ORDER BY NULL) rn FROM sample_data
14 ) PIVOT (MAX(dt) FOR (rn)
15 IN (1 AS Jan_1, 2 AS jan_2, 3 AS Jan_3, 4 AS Feb_1, 5 Feb_2, 6 Feb_3))]',:c);
16 END;
17 /
PL/SQL procedure successfully completed.
Now let's see what Oracle actually does internally:
SQL> set long 100000
SQL> print c
C
--------------------------------------------------------------------------------
SELECT "A1"."JAN_1" "JAN_1",
"A1"."JAN_2" "JAN_2",
"A1"."JAN_3" "JAN_3",
"A1"."FEB_1" "FEB_1",
"A1"."FEB_2" "FEB_2",
"A1"."FEB_3" "FEB_3"
FROM
(SELECT MAX(
CASE WHE N ("A2"."RN"=1)
THEN "A2"."DT"
END ) "JAN_1",
MAX(
CASE
WHEN ("A2"."RN"=2)
THEN " A2"."DT"
END ) "JAN_2",
MAX(
CASE
WHEN ("A2"."RN"=3)
THEN "A2"."DT"
END ) "JAN_3" ,
MAX(
CASE
WHEN ("A2"."RN"=4)
THEN "A2"."DT"
END ) "FEB_1",
MAX(
CASE
WHEN ("A2". "RN"=5)
THEN "A2"."DT"
END ) "FEB_2",
MAX(
CASE
WHEN ("A2"."RN"=6)
THEN "A2"."DT"
END ) "FEB_3"
FROM
(SELECT "A3"."DT" "DT",
ROW_NUMBER() OVER ( ORDER BY NULL) " RN"
FROM (
(SELECT 'Jan' "MNTH",10 "DT" FROM "SYS"."DUAL" "A10"
)
UNION ALL (SE LECT 'Jan' "MNTH",15 "DT" FROM "SYS"."DUAL" "A9")
UNION ALL
(SELECT 'Jan' "MNTH",20 "DT" FROM "SYS"."DUAL" "A8"
)
UNION ALL
(SELECT 'Feb' "MNTH",11 "DT" FROM " SYS"."DUAL" "A7"
)
UNION ALL
(SELECT 'Feb' "MNTH",16 "DT" FROM "SYS"."DUAL" "A6"
)
UNION ALL
(SELECT 'Feb' "MNTH",25 "DT" FROM "SYS"."DUAL" "A5"
)) "A3"
) "A2"
) " A1"

Answer 2

WITH dates( month, day ) AS (
SELECT 'Jan', 10 FROM DUAL UNION ALL
SELECT 'Jan', 15 FROM DUAL UNION ALL
SELECT 'Jan', 20 FROM DUAL UNION ALL
SELECT 'Feb', 11 FROM DUAL UNION ALL
SELECT 'Feb', 16 FROM DUAL UNION ALL
SELECT 'Feb', 25 FROM DUAL
),
ordered_dates( month, day, seq_no ) AS (
SELECT month,
day,
ROW_NUMBER() OVER ( PARTITION BY month ORDER BY day )
FROM dates
)
SELECT MAX( CASE WHEN month = 'Jan' AND seq_no = 1 THEN day END ) AS "Jan",
MAX( CASE WHEN month = 'Jan' AND seq_no = 2 THEN day END ) AS "Jan",
MAX( CASE WHEN month = 'Jan' AND seq_no = 3 THEN day END ) AS "Jan",
MAX( CASE WHEN month = 'Feb' AND seq_no = 1 THEN day END ) AS "Feb",
MAX( CASE WHEN month = 'Feb' AND seq_no = 2 THEN day END ) AS "Feb",
MAX( CASE WHEN month = 'Feb' AND seq_no = 3 THEN day END ) AS "Feb"
FROM ordered_dates;
Output:
Jan Jan Jan Feb Feb Feb
---------- ---------- ---------- ---------- ---------- ----------
10 15 20 11 16 25