How to call variable in select query in oracle

If I understand your question correctly, you're trying to return data from PL/SQL using the query mentioned. While a procedure in SQL Server can return data as a result set, an Oracle procedure cannot do this the same way.

Consider the following example

DECLARE
   n number;
   numvalue number;
   datevalue date;
BEGIN
   n := 10;

   SELECT SYSDATE, n
   FROM dual;
END;
/

This would case an ORA-06550 error since an INTO clause is expected. In other words, you need to return the data to variables.

Note that I didn't use colon before the variable names. Colon is typically used in client side programs to indicate a bind variable, but not inside a PL/SQL block.

Now, if you change the block to the following

DECLARE
   n number;
   numvalue number;
   datevalue date;
BEGIN
   n := 10;

   SELECT SYSDATE, n
   INTO datevalue, numvalue
   FROM dual;

   RAISE_APPLICATION_ERROR(-20001, 'Date: ' || TO_CHAR(datevalue) || ', numvalue: ' || TO_CHAR(numvalue));
END;
/

When the block is executed the query works fine and you can see the result via the custom exception. The result should be

ORA-20001: Date: 10-JAN-20, numvalue: 10

So now the data is known inside the block. In order to return this data to the calling program you have several options. For example you can use a REF_CURSOR, define table type use a pipeline function and so on.

For few examples to return data, have a look at Examples for Creating Oracle Functions[^]