MySQL如果存在则更新一行，如果不存在则更新，以及一般查询建议

I have a personal project which is a browser based game, and I am currently working though old code, and trying to optimise and update everything. I have a lot of functions like the one below, which basically updates the players item amounts. When the item is used, the row is left in the db, but the amount is set to 0, then the amount is updated when the player buys/finds more of that item.I have a personal project which is a browser ba