MySQL 8.0 character set correction

When MySQL is upgraded to version 8.0, the character set of the previous version is often different and needs to be corrected.

By executing the query results of the following three SQL statements , the character set can be corrected from the three levels of library, table, and column.

• Library

  select concat('alter database ', schema_name, ' default character set utf8mb4 collate utf8mb4_general_ci;')
    from information_schema.schemata
   where schema_name not in ('sys', 'mysql', 'performance_schema', 'information_schema')
     and (lower(default_collation_name) != 'utf8mb4_general_ci' or lower(default_character_set_name) != 'utf8mb4');
  

• surface

  select concat('alter table ', table_schema, '.', table_name,
                ' default character set utf8mb4 collate = utf8mb4_general_ci;')
    from information_schema.tables
   where table_schema not in ('sys', 'mysql', 'performance_schema', 'information_schema')
     and table_type = 'BASE TABLE'
     and lower(table_collation) != 'utf8mb4_general_ci';
  

• List

  set group_concat_max_len = 10240;
  
  select concat(c1, c2, ';')
    from (select c1, group_concat(c2) c2
            from (select concat('alter table ', t1.table_schema, '.', t1.table_name) c1,
                         concat(' modify ', '`', t1.column_name, '` ', t1.data_type,
                                if(t1.data_type in ('varchar', 'char'), concat('(', t1.character_maximum_length, ')'),
                                   ''),
                                if(t1.column_default != '', concat(' default \'', t1.column_default, '\''), ''),
                                ' collate utf8mb4_general_ci',
                                if(t1.is_nullable = 'NO', ' not null', ' null'), ' comment ', '''', t1.column_comment,
                                '''')                                                c2
                    from information_schema.columns t1,
                         information_schema.tables t2
                   where t1.table_schema = t2.table_schema
                     and t1.table_name = t2.table_name
                     and t2.table_type = 'BASE TABLE'
                     and (lower(t1.collation_name) != 'utf8mb4_general_ci' or lower(t1.character_set_name) != 'utf8mb4')
                     and t1.table_schema not in ('sys', 'mysql', 'performance_schema', 'information_schema')) t1
           group by c1) t;