Split one column data into multiple columns in oracle - sql

Question

In my oracle query I am using like below for retrieving the records and the result looks like this -
SELECT columnC
, LISTAGG(r.columnA,',') WITHIN GROUP (ORDER BY r.columnB) AS Test_sensor
FROM tableA
GROUP BY columnC
Currently the output looks like below -
ColumnC | Test_Sensor
=============================
Z12345 | 20,30,40,50,60,70
But I want this data to be displayed as below -
ColumnC | Test_Sensor1 | Test_Sensor2 | Test_Sensor3 | Test_Sensor4
==========================================================================
Z12345 | 20 | 30 | 40 | 50
Please help me on this
Thanks
Kranthi RTR

Answer 1

You can use a PIVOT (and do not need to use LISTAGG):
SQL Fiddle
Oracle 11g R2 Schema Setup:
CREATE TABLE TableA ( ColumnA, ColumnB, ColumnC ) AS
SELECT 20, 'A', 'Z12345' FROM DUAL UNION ALL
SELECT 30, 'B', 'Z12345' FROM DUAL UNION ALL
SELECT 40, 'C', 'Z12345' FROM DUAL UNION ALL
SELECT 50, 'D', 'Z12345' FROM DUAL UNION ALL
SELECT 60, 'E', 'Z12345' FROM DUAL UNION ALL
SELECT 70, 'F', 'Z12345' FROM DUAL;
Query 1:
SELECT *
from (
SELECT columnA,
columnC,
ROW_NUMBER() OVER ( PARTITION BY columnC ORDER BY columnB ) AS rn
FROM tableA
) a
PIVOT ( MAX( columnA ) FOR rn IN (
1 AS test_sensor1,
2 AS test_sensor2,
3 AS test_sensor3,
4 AS test_sensor4
) )
Results:
| COLUMNC | TEST_SENSOR1 | TEST_SENSOR2 | TEST_SENSOR3 | TEST_SENSOR4 |
|---------|--------------|--------------|--------------|--------------|
| Z12345 | 20 | 30 | 40 | 50 |
Query 2:
You can do it using LISTAGG but it is much, much less efficient than using PIVOT:
SELECT ColumnC,
REGEXP_SUBSTR( test_sensor, '[^,]+', 1, 1 ) AS test_sensor1,
REGEXP_SUBSTR( test_sensor, '[^,]+', 1, 2 ) AS test_sensor2,
REGEXP_SUBSTR( test_sensor, '[^,]+', 1, 3 ) AS test_sensor3,
REGEXP_SUBSTR( test_sensor, '[^,]+', 1, 4 ) AS test_sensor4
FROM (
SELECT ColumnC,
LISTAGG( ColumnA, ',' ) WITHIN GROUP ( ORDER BY ColumnB )
AS test_sensor
FROM TableA
GROUP BY ColumnC
)
Results:
| COLUMNC | TEST_SENSOR1 | TEST_SENSOR2 | TEST_SENSOR3 | TEST_SENSOR4 |
|---------|--------------|--------------|--------------|--------------|
| Z12345 | 20 | 30 | 40 | 50 |

Answer 2

If you go with LISTAGG, there is a caveat with LISTAGG in that it ignores NULL values. Are you sure your columnA will ALWAYS have data? If, say, test_sensor2 is NULL, the output from the listagg operation will be 20,40,50,60,70 so after the NULL value all sensor's data will be reported wrong! Correct that by using this:
replace(LISTAGG( nvl(to_char(ColumnA), ','), ',' )
WITHIN GROUP ( ORDER BY ColumnB ), ',,,',',,')
Now your output is 20,,40,50,60,70, keeping test_sensor2's NULL value and the rest in proper position.
HOWEVER now there is another problem in that the regex of the form '[^,]+' causes the same issue! So even though the listagg output is fixed, the parsed output is back to being off after the column with the NULL value! There is a different form shown below that fixes this problem. Here is an example set up so you can comment/uncomment to see the differences as the data is processed. Always expect the unexpected!
with TableA ( ColumnA, ColumnB, ColumnC ) AS (
SELECT 20, 'A', 'Z12345' FROM DUAL UNION ALL
SELECT NULL, 'B', 'Z12345' FROM DUAL UNION ALL -- make NULL
SELECT 40, 'C', 'Z12345' FROM DUAL UNION ALL
SELECT 50, 'D', 'Z12345' FROM DUAL UNION ALL
SELECT 60, 'E', 'Z12345' FROM DUAL UNION ALL
SELECT 70, 'F', 'Z12345' FROM DUAL
),
tbl_tmp as (
SELECT ColumnC,
-- Preserve the NULL in position 2
replace(LISTAGG( nvl(to_char(ColumnA), ','), ',' )
WITHIN GROUP ( ORDER BY ColumnB ), ',,,',',,')
AS test_sensor
FROM TableA
GROUP BY ColumnC
)
--select * from tbl_tmp;
-- regex of format [^,]+ does not handle NULLs
SELECT ColumnC,
-- REGEXP_SUBSTR( test_sensor, '[^,]+', 1, 1) AS test_sensor1,
-- REGEXP_SUBSTR( test_sensor, '[^,]+', 1, 2 ) AS test_sensor2,
-- REGEXP_SUBSTR( test_sensor, '[^,]+', 1, 3 ) AS test_sensor3,
-- REGEXP_SUBSTR( test_sensor, '[^,]+', 1, 4 ) AS test_sensor4
REGEXP_SUBSTR( test_sensor, '(.*?)(,|$)', 1, 1, NULL, 1) AS test_sensor1,
REGEXP_SUBSTR( test_sensor, '(.*?)(,|$)', 1, 2, NULL, 1 ) AS test_sensor2,
REGEXP_SUBSTR( test_sensor, '(.*?)(,|$)', 1, 3, NULL, 1 ) AS test_sensor3,
REGEXP_SUBSTR( test_sensor, '(.*?)(,|$)', 1, 4, NULL, 1 ) AS test_sensor4
FROM tbl_tmp;