avoid 'IF' , if possible to check different condition in where clause

I have a query in which column used in where clause in changed depending on the parameter of the stored procedure:

select * from tableName where col2=someValue 

above query runs if inputparameter is 'X' and if it is 'Y' then

select * from tableName where col2=someValue 

I can write a if block checking for the condit开发者_如何转开发ion and then executing the respective query. but i am trying to combine these two query into one. Please help.

SELECT * from tableName 
WHERE  ( inputparameter = 'X' AND  col1=someValue )
    OR ( inputparameter = 'Y' AND  col2=someValue )
       ;

WHERE :SomeValue = DECODE(:InputParameter, 'X', Col1, 'Y', Col2)

select * from tableName 
where  1 = CASE
            when inputparameter = 'X'
            AND  col1=someValue 
            THEN 1
            when inputparameter = 'Y'
            AND  col2=someValue 
            THEN 1
            ELSE 0
           END

All solutions built around conditions in "where" part of query are working, but not optimal from performance point of view. Therefore, if tableName is really big then better variant is building dynamic sql or implement this case as two separate query.

E.g.

create or replace procedure GetSomething(
  inputParameter in varchar2, 
  someValue      in varchar2  
) 
  return sys_refcursor
as
  cRet sys_refcursor;
begin

  if(inputParam = 'X') then
    open cRet for 
       select * from tableName where col1 = someValue
    ;
  elsif(inputParam = 'Y') then
    open cRet for 
       select * from tableName where col2 = someValue
    ;
  else
    raise_application_error(-20001,'Invalid value of inputParameter.'); 
  end if;

end;

Of course, both columns must be indexed for good performance.