Differences between drop user and delete from mysql. user

Drop user deletes all user information, while delete only deletes the user table. Other information, such as the information in the db table, still exists.
If you create a user with the minimum permission after the delete operation, the user will reuse the previous permissions.
Grant all on test. * to 'test' @ '%' identified by 'test ';
Delete from user where user = test;
Db tables
Mysql> select * from db;
+ ------ + --------- + ------ + Upper + ------------- + ----------- + ------------- + upper + ----------- + ------------ + upper + ------------ + ---------- + upper + lower + -------------- + ------------ + -------------- +
| Host | Db | User | Select_priv | response | Update_priv | Delete_priv | Create_priv | Drop_priv | Grant_priv | response | Index_priv | Alter_priv | response | Execute_priv | Event_priv | Trigger_priv |
+ ------ + --------- + ------ + Upper + ------------- + ----------- + ------------- + upper + ----------- + ------------ + upper + ------------ + ---------- + upper + lower + -------------- + ------------ + -------------- +
| % | Test | Y | N | Y |
| % | Test \ _ % | Y | N | N | Y |
| % | Test | Y | N | Y | Y |
+ ------ + --------- + ------ + Upper + ------------- + ----------- + ------------- + upper + ----------- + ------------ + upper + ------------ + ---------- + upper + lower + -------------- + ------------ + -------------- +
3 rows in set (0.00 sec)
The test permission still exists.
Create a select-only user test
Grant select on test. * to 'test' @ '% 'identified by 'test ';
Mysql> select * from db;
+ ------ + --------- + ------ + Upper + ------------- + ----------- + ------------- + upper + ----------- + ------------ + upper + ------------ + ---------- + upper + lower + -------------- + ------------ + -------------- +
| Host | Db | User | Select_priv | response | Update_priv | Delete_priv | Create_priv | Drop_priv | Grant_priv | response | Index_priv | Alter_priv | response | Execute_priv | Event_priv | Trigger_priv |
+ ------ + --------- + ------ + Upper + ------------- + ----------- + ------------- + upper + ----------- + ------------ + upper + ------------ + ---------- + upper + lower + -------------- + ------------ + -------------- +
| % | Test | Y | N | Y |
| % | Test \ _ % | Y | N | N | Y |
| % | Test | Y | N | Y | Y |
+ ------ + --------- + ------ + Upper + ------------- + ----------- + ------------- + upper + ----------- + ------------ + upper + ------------ + ---------- + upper + lower + -------------- + ------------ + -------------- +
3 rows in set (0.00 sec)
The permission is the same as before.