Creating resultset based on column name defined in another table in Oracle - sql

Question

In Oracle database, I have a table DATA_DUMP_TABLE which has generic column names
id column1 column2 column3 column4 column5 def_id
1 John Doe null null null 1
2 Tom Baker null null null 1
Then I have a metadata table COLUMN_DEF which defines the data column names. It could vary based on the definition id. Say in this case I just want to map the first 2 columns.
def_id mapped_column mapped_column_val`
1 column1 First Name
1 column2 Last Name
The resultset I am expecting is based on the mapped_column_val from COLUMN_DEF table
So, in this case the resultset would look like this
id First Name Last Name
1 John Doe
2 Tom Baker
How do I achieve this in oracle, whether this could be done via SQL or I have to use advance packages? Any help would be appreciated.

Answer 1

It Works with sql server.
DECLARE #new_names as nvarchar(MAX)
DECLARE #sql as nvarchar(MAX)
SELECT #new_names = STRING_AGG('[' + MAPPED_COLUMN_VAL + ']', ',') FROM COLUMN_DEF
SET #sql = 'SELECT * FROM (
SELECT t.ID, t.COLUMN_VALUES, t.DEF_ID, c.MAPPED_COLUMN_VAL FROM (
SELECT ID, COLUMN_NAME, COLUMN_VALUES, DEF_ID
FROM
(SELECT * FROM DUMP_DATA) d
UNPIVOT
(
COLUMN_VALUES FOR COLUMN_NAME IN
(COLUMN1, COLUMN2, COLUMN3, COLUMN4, COLUMN5)
) unpvt
) AS t LEFT OUTER JOIN
COLUMN_DEF c ON t.COLUMN_NAME = c.MAPPED_COLUMN
) b
PIVOT
(
MAX(COLUMN_VALUES) FOR MAPPED_COLUMN_VAL IN ( ' + #new_names + ' )
--IN ([FIRST NAME], [LAST NAME])
) AS pivot_table;'
EXEC dbo.SP_EXECUTESQL #sql
Unpivot Will remove columns with NULL values.
INPUT:
ID COLUMN1 COLUMN2 COLUMN3 COLUMN4 COLUMN5 DEF_ID
1 JOHN DOE NULL NULL NULL 1
2 TOM BAKER NULL NULL NULL 2
DEF_ID MAPPED_COLUMN MAPPED_COLUMN_VAL
1 COLUMN1 FIRST NAME
2 COLUMN2 LAST NAME
RESULT:
ID DEF_ID FIRST NAME LAST NAME
1 1 JOHN DOE
2 2 TOM BAKER

Answer 2

In general I think that this requires pl/sql and dynamic SQL as stated by #gordon-linoff
This is gets very close.
Create table temp_sgc1(id number, column1 Varchar2(20), column2 varchar2(20));
Insert into temp_sgc1 values(1 , 'John' , 'Doe');
Insert into temp_sgc1 values(2 , 'Tom' , 'Baker');
Create table temp_sgc2(def_id number, mapped_column Varchar2(20), mapped_column_va
l
varchar2(20));
Insert into temp_sgc2 values(1, 'column1', 'First Name');
Insert into temp_sgc2 values(1, 'column2', 'Last Name');
Select * from
(select * from temp_sgc2
pivot (
max(mapped_column_val) for mapped_column in ( 'column1' column1, 'column2' column2 )
)
order by def_id)
union all
Select id, column1, column2
from temp_sgc1
;
RESULT:
DEF_ID COLUMN1 COLUMN2
1 First Name Last Name
1 John Doe
2 Tom Baker