Php+mysql How to prevent the situation of inventory being oversold due to concurrency

Php+mysql how to prevent concurrency causing inventory to be oversold.
Site encounters such as group purchase, second kill, special events such as the time, but inventory is limited, the current situation is, if a commodity has only one inventory, at this time there are two users at the same time, the inventory will become 1, also shows that two users have bought, but I have only one inventory, how to solve this problem?
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Database lock, select for update:
Control inventory with cache. Every time decrement ... After the order is not paid back again set back
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1. Handling of Things
In general, transaction processing can be resolved, I use this side is basically this


2. Each reduction of inventory corresponding to an order serial number (this order serial number in the generation of reduced inventory this user action will be generated), the order serial number is the table of self-increment ID, and then statistics this water, it is good to solve it!

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