How do I get the data from the column_name? Oracle PL/SQL - oracle

Question

How do I get the data(i.e rows) from the column_name I retrieved from SQL statement? (Completely new to PL/SQL).
Here is my code:
create or replace procedure com_coll_cur
as
type comColcur is ref cursor;
com_col_cur comColcur;
sql_stmt varchar2(4000);
type newtab_field is table of comColcur%TYPE;
begin
sql_stmt :=
'select column_name from all_tab_cols where table_name in (''TAB1'', ''TAB2'') ' ||
'group by column_name having count(*)>1';
open com_col_cur for sql_stmt;
loop
fetch com_col_cur into newtab_field;
exit when com_col_cur%NOTFOUND;
end loop;
close com_col_cur;
end;
What I'm trying to do here is first find the common columns between the two tables. This part only grabs column_name but I also want the data in that common columns. So I used cursor to "point" that common column_name and used loop(fetch) to get the data inside that common column_name. Finally, I want to create new table with this common columns only with their data.
I am new to everything here and any help will be appreciate it.

Answer 1

You don't understand how works cursors and fetch.
Fetch get the data from the cursor, so in your procedure example you get only column names, not the data in the columns. To get data you need another cursor - select from the target table or use the dynamic sql.
This is a code that do what you describe. It is not clear to me how you want to store data from two tables - subsequently or in another manner. Let's assume that we store them subsequently. Also this code suggests than columns with the same names have the same datatypes. Part of this code (to make datatype) I get from another stackoverflow post to save time to write it:
How do I get column datatype in Oracle with PL-SQL with low privileges?
dbms_output.put_line - used to print sql statements that we create
declare
cSql varchar2(4000);
cCols varchar2(4000);
cNewTableName varchar2(30) := 'AABBCC';
cTb1 varchar2(30) := 'TAB1';
cTb2 varchar2(30) := 'TAB2';
begin
for hc in (
select T.column_name, T.typ
from
(
select column_name,
data_type||
case when data_precision is not null and nvl(data_scale,0)>0 then '('||data_precision||','||data_scale||')'
when data_precision is not null and nvl(data_scale,0)=0 then '('||data_precision||')'
when data_precision is null and data_scale is not null then '(*,'||data_scale||')'
when char_length>0 then '('||char_length|| case char_used
when 'B' then ' Byte'
when 'C' then ' Char'
else null
end||')'
end||decode(nullable, 'N', ' NOT NULL') typ
from all_tab_cols
where table_name in (cTb1, cTb2) ) T
group by T.column_name, T.typ having count(*) > 1)
loop
cSql := cSql || case when cSql is null then null else ',' end || hc.column_name || ' ' || hc.typ;
cCols := cCols || case when cCols is null then null else ',' end || hc.column_name;
end loop;
if (cSql is not null) then
-- First drop table if it exists
for hc in (select * from all_objects where object_type = 'TABLE' and object_name = cNewTableName)
loop
execute immediate 'drop table ' || hc.object_name;
end loop;
-- create table
cSql := 'create table ' || cNewTableName || '(' || cSql || ')';
dbms_output.put_line(cSql);
execute immediate cSql;
-- insert data
cSql := 'insert into ' || cNewTableName || '(' || cCols || ') select ' || cCols || ' from ' || cTb1;
dbms_output.put_line(cSql);
execute immediate cSql;
cSql := 'insert into ' || cNewTableName || '(' || cCols || ') select ' || cCols || ' from ' || cTb2;
dbms_output.put_line (cSql);
execute immediate cSql;
end if;
end;