The SQL file of mysql8.0 was imported into version 5.5. There was a pit

first ： Character encoding problem

error ：

Unknown collation: ‘utf8mb4_0900_ai_ci‘......

resolvent ：
Manually modify sql file ：

utf8mb4_0900_ai_ci Replace all with utf8_general_ci
utf8mb4 Replace with utf8

the second ：TIMESTAMP Type problem

error ：

Incorrect table definition; there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT 

The reason is when you give a timestamp Set to on updatecurrent_timestamp When , Other timestamp Fields need to be explicitly set default value . But if you have two timestamp Field , Set only the first to current_timestamp And the second one doesn't have a default , You're going to report a mistake
resolvent ：
Set default values for several other fields ：

 DEFAULT '0000-00-00 00:00:00' 

Third ： Character length problem ：

error ：

Specified key was too long; max key length is 767 bytes

resolvent ：
stay utf-8 Character set ,255 success ,utf-8 One character takes up 3 Bytes ,255*3=765 mysql5.6 The longest index is 767.