Simple trigger consult, after up to judge the value, and then modify a value

Everyone is very good, recently just contacted PHP and MySQL know that MySQL has a trigger, there is a small program need to automatically determine the value to modify another field value, to be implemented by a trigger, or by the way to learn the trigger. So come to ask you a big,
So, the user table has 2 fields, one is Jifen, the other is Dengji,
The trigger needs to be judged when the Jifen changes:
If Jifen is greater than or equal to 5000 Dengji is 2,
If Jifen is greater than or equal to 10000 Dengji is 3,

is in a table, do not know the trigger can be implemented? How does a trigger write?

Reply to discussion (solution)

Landlord this situation does not need to use the trigger Ah, you are not just want to test, it is recommended to learn the basics of flip-flop is good.

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