A320 flight crew on final approach reported main gear not down and locked.

Narrative

While on final approach the FO called for the gear down and I (PM) selected the landing gear down. At about 1;500 feet the nose gear and right main gear were down. However; we got an indication that the left gear door was open. That was followed by the left gear showing unlocked on both the ECAM and landing gear panel.At this time; we advised the tower we would like to execute a missed approach. We had several seconds to discuss what we would do and then we went around. We elected to keep the landing gear down. On the go-round; tower; advised us that the left gear did look down. Also while on the go-around; the left gear door closed and the left gear went from unlocked to down and locked and green.Who are you contacted ZZZ departure and they vectored us for a close and left downwind. ZZZ1 Tower was able to visually inspect our gear and didn't say it. It looked down. We continued on and landed visually in ZZZ1 with no further incident.However; after landing; received a caution for landing gear system disagree. I wrote this all up in the logbook and maintenance met the aircraft at the gate.