Oracle 12c - SQL string build issue - sql

Question

This is a follow up to a previous question: Dynamically build select statement in Oracle 12c
I am trying to build a select statement dynamically but having a problem building the column alias names. The column alias name must be retrieved from MAIN_TABLE. Please refer to the code inside <> below:
declare
upper_level number;
t_sql varchar2(1000);
t_sql_val varchar2(500);
l_sql varchar2(1000);
begin
--upper_level will always be given
select 3 into upper_level from dual;
--build the fixed string
l_sql:='SELECT ID,
Title,
Desc,
Type,';
for lvl in 1..upper_level
loop
--build the column names and alias names
t_sql:=t_sql||'TYPE_'||lvl||' <SELECT TYPE_'||lvl||' FROM MAIN_TABLE WHERE ID = 1>,';
end loop;
--finish building the statement
t_sql:=rtrim(t_sql,',');
l_sql:=l_sql||t_sql;
l_sql:=l_sql||' FROM SCHEMA.TABLE
WHERE ID = 1;';
--dbms_output.put_line(l_sql);
end;
This was my attempt:
declare
upper_level number;
t_sql varchar2(1000);
v_sql varchar2(1000);
v_sql_val varchar2(1000);
t_sql_val varchar2(500);
l_sql varchar2(1000);
begin
--upper_level will always be given
select 3 into upper_level from dual;
--build the fixed string
l_sql:='SELECT ID,
Title,
Desc,
Type,';
for lvl in 1..upper_level
loop
--build the column names and alias names
t_sql:='TYPE_'||lvl||;
v_sql:='SELECT '||t_sql||' FROM MAIN_TABLE WHERE ID=1';
EXECUTE IMMEDIATE v_sql into v_sql_val;
t_sql:=t_sql||' '||v_sql_val||',';
end loop;
--finish building the statement
t_sql:=rtrim(t_sql,',');
l_sql:=l_sql||t_sql;
l_sql:=l_sql||' FROM SCHEMA.TABLE
WHERE ID = 1;';
dbms_output.put_line(l_sql);
end;
My attempted result:
SELECT ID,
Title,
Desc,
Type,TYPE_3 LVL_3 FROM SCHEMA.TABLE
WHERE ID = 1;
My expected result:
SELECT ID,
Title,
Desc,
Type,TYPE_1 LVL_1, TYPE_2 LVL_2, TYPE_3 LVL_3 FROM SCHEMA.TABLE
WHERE ID = 1;
How can I achieve this?

Answer 1

I have figured out how to achieve expected result:
declare
upper_level number;
t_sql varchar2(1000);
v_sql varchar2(1000);
v_sql_val varchar2(1000);
t_sql_val varchar2(500);
l_sql varchar2(1000);
begin
--upper_level will always be given
select 3 into upper_level from dual;
--build the fixed string
l_sql:='SELECT ID,
Title,
Desc,
Type,';
for lvl in 1..upper_level
loop
--build the column names and alias names
t_sql:=t_sql||'TYPE_'||lvl||'_CD';
v_sql:='SELECT TYPE_'||lvl||'_CD FROM MAIN_TABLE WHERE ID=1';
EXECUTE IMMEDIATE v_sql into v_sql_val;
t_sql:=t_sql||' '||v_sql_val||',';
end loop;
--finish building the statement
t_sql:=rtrim(t_sql,',');
l_sql:=l_sql||t_sql;
l_sql:=l_sql||' FROM SCHEMA.TABLE
WHERE ID = 1;';
dbms_output.put_line(l_sql);
end;