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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.schematawhere 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.tableswhere 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) c2from (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,'''')                                                c2from information_schema.columns t1,information_schema.tables t2where t1.table_schema = t2.table_schemaand t1.table_name = t2.table_nameand 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')) t1group by c1) t;