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.