sqlplus SELECT from the selected result - sql

Question

I am using Oracle sqlplus and am trying to use the result being selected from the codes below and select the column again from Table_1
SELECT *
FROM
(
SELECT Column_Name
FROM All_Tab_columns
WHERE Table_Name=UPPER('Table_1')
)
INTERSECT
(
SELECT Column_Name
FROM All_Tab_columns
WHERE Table_Name=UPPER('Table_2')
);
How can I perform something like that:
SELECT <Columns_That_Intersected>
FROM Table_1;
Is it possible to store the Columns_That_Intersected in a variable/function/procedure and use it again for other select statement?

Answer 1

Yes, it's possible. Just save the aggregated result of the query in a substitution variable. Something like this:
create table items1 as
select rownum id, 'me '||rownum name, 1 dummy
from xmlTable ('1 to 3');
create table items2 as select id, name from items1;
set verify off
col Columns_That_Intersected new_value Columns_That_Intersected noprint
select listagg (column_name, ',') within group (order by null) Columns_That_Intersected
from (
select column_name
from All_Tab_Columns
where Table_Name=UPPER('items1')
intersect
select column_name
from All_Tab_columns
where Table_Name=UPPER('items2')
);
prompt Columns_That_Intersected=&Columns_That_Intersected
select &Columns_That_Intersected
from items1;
Output:
Columns_That_Intersected=ID,NAME
ID NAME
---------- -------------------------------------------
1 me 1
2 me 2
3 me 3
About col[umn] command

Answer 2

Just to fetch the column names which exists in both the table table1 and table2, you can use below query:
SELECT Column_Name
FROM all_tab_columns t1
WHERE table_name = 'Table1'
AND EXISTS (SELECT 1
FROM all_tab_columns t2
WHERE table_name = 'Table2'
AND t2.Column_Name = t1.Column_Name);
Then to fetch these column values from Table1, you can use below PL/SQL construct:
DECLARE
v_sql_statement VARCHAR2(2000);
v_cols VARCHAR2(2000);
BEGIN
FOR cn IN (SELECT Column_Name
FROM all_tab_columns t1
WHERE table_name = 'Table1'
AND EXISTS (SELECT 1
FROM all_tab_columns t2
WHERE table_name = 'Table2'
AND t2.Column_Name = t1.Column_Name))
LOOP
v_cols := v_cols || ', ' || cn.column_name;
END LOOP;
v_cols := ltrim(v_cols, ',');
v_sql_statement := 'SELECT ' || v_cols || ' FROM Table1';
EXECUTE IMMEDIATE v_sql_statement;
END;

Answer 3

you can, for example, work with a dynamic sql.
The result of your selects can be aggregated to a list using the listagg function
SELECT listagg( Column_Name,',') WITHIN GROUP (ORDER BY 1) cols
FROM
(
SELECT Column_Name
FROM All_Tab_columns
WHERE Table_Name=UPPER('tab1')
INTERSECT
SELECT Column_Name
FROM All_Tab_columns
WHERE Table_Name=UPPER('tab2')
);
As result you get then eg. col1, col2, col3
with the help of this list you can then create a cursor in a plsql block and then loop through it to print out wat you want.
declare
v_cols VARCHAR2(2000);
v_select_string varchar(2000);
csr SYS_REFCURSOR;
v1 VARCHAR2(2000);
BEGIN
SELECT listagg( Column_Name,',') WITHIN GROUP (ORDER BY 1) cols
into v_cols
FROM
(
SELECT Column_Name
FROM All_Tab_columns
WHERE Table_Name=UPPER('tab1')
INTERSECT
SELECT Column_Name
FROM All_Tab_columns
WHERE Table_Name=UPPER('tab2')
);
v_select_string := 'SELECT ' || v_cols ||
' FROM tab1';
OPEN csr FOR v_select_string;
LOOP
FETCH csr INTO v1;
EXIT WHEN csr%NOTFOUND;
DBMS_OUTPUT.PUT_LINE( v1);
END LOOP;
CLOSE csr;
END P1;