If I Knew by Bruno Mars is in Ab at 87 beats per minute and runs 2:06 across 45 bars. It uses 13 chords — Eb, Bb, Ab, Abm, Cm7, Fm7, Eb7, F, and a few more. The chord diagram changes as the song plays and the words light up as they are sung, so you can strum and sing along without reading ahead.
Want the melody line note by note? If I Knew guitar melody tab.