Informix is not Oracle
And AFAIK the way you wrote your sql is not possible in oracle too.(just simple concatenate two strings without appropriate function- e.g. execute immediate or other method)

What you are trying to do is called dynamic sql...which Informix supports only in version 11.5 (the newest version).
This feature had no support in earlier versions in built-in SQL or SPL. Instead you can use 4GL or ESQL for this purpose. Another way is use Exec datablade(provides equivalent to oracle 'execute immediate'), but this datablade is "out of the box" -open source and has no support or warranty from IBM.