Oracle Create Function - oracle

Question

I tried to create an Oracle function where table name, column name and where string are dynamic parameters:
CREATE OR REPLACE FUNCTION MYSCHEMA.myFunctionName(
tableName in nvarchar2,
columnName in nvarchar2,
whereStr in nvarchar2)
RETURN nvarchar2
IS nActive nvarchar2(2000);
BEGIN
declare
querystr nvarchar2(2000) ;
result nvarchar2(2000);
begin
querystr :='
select listagg('+columnName+','+','+') within group (order by '+columnName+')
from '+tableName+' where 1 = 1 '+whereStr+';';
EXECUTE IMMEDIATE querystr
INTO result;
nActive := result;
RETURN ( nActive );
end;
END ;
/
But it gives me error "Warning: compiled but with compilation errors".
What am I doing wrong?

Answer 1

For concatenate strings in Oracle use || not +
You don't need ; at the end of execute immediate query string
You need to escape ' using ''.
... as #Aleksej said
Execute immediate need query string in CHAR or VARCHAR2;
listagg return either raw or VARCHAR2
CREATE OR REPLACE FUNCTION MYSCHEMA.myFunctionName(
tableName in varchar2,
columnName in varchar2,
whereStr in varchar2)
RETURN varchar2
BEGIN
declare
querystr varchar2(2000) ;
result varchar2(2000);
begin
querystr :='
select listagg('|| columnName || ', '','') within group (order by ' ||columnName ||')
from ' || tableName || ' where 1 = 1 ' || whereStr;
EXECUTE IMMEDIATE querystr INTO result;
return result;
end;
END ;
/

Answer 2

You need to change the type of your variables, considering that
"The return data type is RAW if the measure column is RAW; otherwise the return value is VARCHAR2" (documentation)
EXECUTE needs a VARCHAR2: "It must be of type CHAR or VARCHAR2, not NCHAR or NVARCHAR2"
So:
declare
querystr varchar2(2000) ;
result VARCHAR2(32767);
begin
...