F9-004: Primary mission success, secondary mission scrubbed due to ISS safety rules
F9-006: Success (first v1.1 flight)
F9-009: Success (first flight with landing legs)
F9-020: Failure, RUD at T+150s
F9-021: Success, first v1.1 FT, first successful landing at Canaveral
F9-023: Success, first successful landing on droneship
One failure. Out of twenty-seven, for a success rate of 96%. Unless you want to count landings as necessary for success, in which case they have a 19% success rate - but by that metric, Soyuz, Proton, Atlas, Delta, Titan, Redstone, Saturn, Ariane, Athena, and Zenit all have 0% success rates, and only Energia-Buran and STS also have a non-zero success rate, with 50% and 98%, respectively.
Over that same period North Korea fired four missiles (claiming to have fired even more but not supported by evidence) and launched two orbital rockets. The missiles may or may not have failed - they fell vastly short of their design range but that may have been deliberate - and both rockets worked, although their payloads may have failed. At least, this is all the info I could find - there's no convenient list of every launch attempt they've made, and I suspect most failed launches are never revealed.