When there is a written piano part, it is scored on two staffs, separate from the vocal parts. If the vocal parts are drawn from the Lead Sheet (written on a single staff), then the Piano/Vocal would be three staffs: bass and treble clef for the piano, and then the treble clef for the lead sheet written on top of that. If the vocal parts are written in SATB, then the Piano/Vocal would be four staffs: bass and treble clef for the piano, and then bass (bass and tenor) and treble (alto and soprano) clef for the vocals. This way, the piano part can be written totally independently from the vocal lines. This makes for a better written piano part that is not tied to the melody.
To see a complete list of songs in our catalog that have piano parts, go to the Song List page and click on the Piano/Vocal checkbox under Search Filters in the left sidebar. That will narrow the list of titles down to only those that have piano parts available.