MySQL 8.0字符集校正

MySQL升级为8.0版本时，之前版本的字符集往往是不同的，需要校正。

执行下面的三个SQL语句的查询结果，可以从库、表、列三个层面对字符集进行校正。

• 库

  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');
  

• 表

  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';
  

• 列

  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;