Fetch all columns into one column oracle - sql

Question

How do i achieve to fetch all columns into one column.
I have below sample query
WITH da AS(
SELECT 'a' col1, 'b' col2, 'c' col3 FROM dual UNION ALL
SELECT '1' col1, '2' col1, '3' col1 FROM dual UNION ALL
SELECT 'x' col1, 'y' col1, 'z' col1 FROM dual
)
SELECT * FROM da;
//RESULTS
COL1|COL2|COL3|
----|----|----|
a |b |c |
1 |2 |3 |
x |y |z |
But what i want is the result to be as below with | as the delimiter.
ONE_COL|
-------|
a|b|c |
1|2|3 |
x|y|z |
My biggest problem is i don't know the column names, therefore i cant do as:
SELECT col1||'|'||col2||'|'||col3 AS ONE_COL FROM da;
how can i do this.

Answer 1

The following is just to demonstrate a way to achieve what you asked for. (Assuming I didn't misunderstand what you asked for.)
First some preparation.
Create the DA table (according to the sample data in your question).
create table DA (COL1 char(1), COL2 char(1), COL3 char(1));
Add rows to the table (again, according to the sample data in your question).
insert into DA values ('a','b','c');
insert into DA values ('1','2','3');
insert into DA values ('x','y','z');
I understand that you want to insert the data from table DA into another table, so I created a second database table according to what I understood from your question.
create table RESULT (ONE_COL char(5));
PL/SQL code that retrieves the names of the columns (assuming you know the table name) from the data dictionary, then creates a dynamic cursor to retrieve the values from that table (again in the format described in your question) and inserts the rows fetched by the dynamic cursor into a second database table (since this is your requirement as I understood it from your question).
declare
L_COL varchar2(128);
L_CUR sys_refcursor;
L_ONE char(5);
L_SQL varchar2(2000);
--
cursor C_COLS is
select COLUMN_NAME
from USER_TAB_COLUMNS
where TABLE_NAME = 'DA';
begin
L_SQL := 'select ';
open C_COLS;
fetch C_COLS into L_COL;
L_SQL := L_SQL || L_COL;
while C_COLS%found
loop
fetch C_COLS into L_COL;
if C_COLS%found then
L_SQL := L_SQL || '||';
L_SQL := L_SQL || '''|''||';
L_SQL := L_SQL || L_COL;
end if;
end loop;
close C_COLS;
L_SQL := L_SQL || ' from DA';
open L_CUR for L_SQL;
loop
fetch L_CUR into L_ONE;
exit when L_CUR%notfound;
insert into RESULT values (L_ONE);
end loop;
close L_CUR;
end;
Finally, after running the above PL/SQL code...
select * from RESULT;
which returns
ONE_C
-----
abc
123
xyz

Answer 2

Concat the dual columns within the with clause, that way you don't need know what the da columns are called.
WITH da AS(
SELECT 'a' || '|' || 'b' || '|' || 'c' AS one_col FROM dual UNION ALL
SELECT '1' || '|' || '2' || '|' || '3' AS one_col FROM dual UNION ALL
SELECT 'x' || '|' || 'y' || '|' || 'z' AS one_col FROM dual
)
SELECT * FROM da;

Answer 3

The database knows the column names. So use the dbms_sql package and parse your sql.
https://docs.oracle.com/en/database/oracle/oracle-database/19/arpls/DBMS_SQL.html#GUID-C96D5BAA-29A9-4AB5-A69E-E31228ECC9E9
There are many solutions to extract the data afterwards so I don't get your point why you think that you don't know any column names