Mysql中索引和约束的示例语句

外键

查询一个表的主键是哪些表的外键

select
	table_name,
	column_name,
	constraint_name,
	referenced_table_name,
	referenced_column_name
from
	information_schema.key_column_usage
where
	table_schema = 'mydbname'
	and referenced_table_name = '表名';

导出所有外键语句

select
	concat('alter table ', table_name, ' add constraint ', constraint_name, ' foreign key (', column_name, ') references ', referenced_table_name, '(', referenced_column_name, ') on delete cascade on update cascade;')
from
	information_schema.key_column_usage
where
	table_schema = 'mydbname'
	and referenced_table_name is not null;

删除所有外键语句

select
	concat('alter table ', table_name, ' drop foreign key ', constraint_name, ';')
from
	information_schema.key_column_usage
where
	table_schema = 'mydbname'
	and referenced_table_name is not null;

自增

导出创建自增字段的语句

select
	concat( 'alter table `', table_name, '` ', 'modify column `', column_name, '` ', upper( column_type ), ' not null auto_increment comment "',column_comment,'";' ) as 'add_auto_increment'
from
	information_schema.columns 
where
	table_schema = 'mydbname' 
	and extra = upper( 'auto_increment' ) 
order by
	table_name asc;

创建删除所有自增字段

select
	concat( 'alter table `', table_name, '` ', 'modify column `', column_name, '` ', upper( column_type ), ' not null;' ) as 'delete_auto_increment'
from
	information_schema.columns 
where
	table_schema = 'mydbname' 
	and extra = upper( 'auto_increment' ) 
order by
	table_name asc;

索引

导出所有索引

select
	concat(
		'alter table `',
		table_name,
		'` ',
		'add ',
	if
		(
			non_unique = 1,
		case
				upper( index_type ) 
				when 'fulltext' then
				'fulltext index' 
				when 'spatial' then
				'spatial index' else concat( 'index `', index_name, '` using ', index_type ) 
			end,
		if
			(
				upper( index_name ) = 'primary',
				concat( 'primary key using ', index_type ),
			concat( 'unique index `', index_name, '` using ', index_type ))),
		concat( '(`', column_name, '`)' ),
		';' 
) as 'add_all_index' 
from
	information_schema.statistics 
where
	table_schema = 'mydbname' 
order by
	table_name asc,
	index_name asc;

删除所有索引

select
	concat( 'alter table `', table_name, '` ', concat( 'drop ', if ( upper( index_name ) = 'primary', 'primary key', concat( 'index `', index_name, '`' ))), ';' ) as 'delete_all_index' 
from
	information_schema.statistics 
where
	table_schema = 'mydbname' 
order by
	table_name asc;

数据合并

在数据迁移合并的时候，比较棘手的是不同数据库主键重复，那么我们就要批量修改主键的值，为了避免重复我们可以把自增的数字改为字符串

步骤基本上有以下几步

• 取消主键自增
• 删除所有外键
• 修改主键字段为varchar
• 添加所有外键
• 修改主键的值
• 合并数据
  

修改主键值的时候要注意

如果包含id和pid这种自关联的情况下是不能直接修改值的，就需要先删除约束再添加。

比如

删除自约束

alter table `t_director` drop foreign key `fk_directorpid`;

修改值

update t_director set directorid=directorid+100000000;
update t_director set directorid=conv(directorid,10,36);

update t_director set directorpid=directorpid+100000000 where directorpid is not null;
update t_director set directorpid=conv(directorpid,10,36) where directorpid is not null;

添加自约束

alter table t_director add constraint fk_directorpid foreign key (directorpid) references t_director(directorid) on delete cascade on update cascade;

注意

conv(directorpid,10,36)后两个参数为原数字进制和要转换后的进制。

第一个参数只要内容是数字就算类型为varchar也可以转换。

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