对比两个库表结构

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##判断两个数据库相同表的字段不为空是否相同
select a.TABLE_SCHEMA,a.TABLE_NAME,a.COLUMN_NAME,a.COLUMN_TYPE,a.IS_NULLABLE,a.COLUMN_DEFAULT,b.TABLE_SCHEMA,b.TABLE_NAME,b.COLUMN_NAME,b.COLUMN_TYPE,b.IS_NULLABLE ,b.COLUMN_DEFAULT,b.COLUMN_COMMENT 
from information_schema.`COLUMNS` a inner join information_schema.`COLUMNS` b 
on a.TABLE_SCHEMA='db1' and b.TABLE_SCHEMA='db2'and a.TABLE_NAME=b.TABLE_NAME and a.COLUMN_NAME=b.COLUMN_NAME and a.IS_NULLABLE<>b.IS_NULLABLE
where a.IS_NULLABLE='NO';
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##判断两个数据库相同表的字段默认值是否相同
select a.TABLE_SCHEMA,a.TABLE_NAME,a.COLUMN_NAME,a.COLUMN_DEFAULT,b.TABLE_SCHEMA,b.TABLE_NAME,b.COLUMN_NAME,b.COLUMN_DEFAULT from information_schema.`COLUMNS` a 
inner join information_schema.`COLUMNS` b on a.TABLE_SCHEMA='db1' and b.TABLE_SCHEMA='db2'
and a.TABLE_NAME=b.TABLE_NAME and a.COLUMN_NAME=b.COLUMN_NAME and a.COLUMN_DEFAULT<>b.COLUMN_DEFAULT;

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##判断两个数据库相同表的字段数据类型是否相同,这里是判断数据类型不同如果要判断数据类型的长度不同需要用COLUMN_TYPE字段
select a.TABLE_SCHEMA,a.TABLE_NAME,a.COLUMN_NAME,a.DATA_TYPE,a.COLUMN_DEFAULT,b.TABLE_SCHEMA,b.TABLE_NAME,b.COLUMN_NAME,b.DATA_TYPE ,b.COLUMN_DEFAULT
from information_schema.`COLUMNS` a inner join information_schema.`COLUMNS` b on a.TABLE_SCHEMA='db1' and b.TABLE_SCHEMA='db2'
and a.TABLE_NAME=b.TABLE_NAME and a.COLUMN_NAME=b.COLUMN_NAME and a.DATA_TYPE<>b.DATA_TYPE;

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##判断两个数据库相同表的中互相不存在的字段
select a.TABLE_SCHEMA,a.TABLE_NAME,a.COLUMN_NAME,a.DATA_TYPE,a.COLUMN_DEFAULT
from information_schema.`COLUMNS` a 
where a.TABLE_SCHEMA='db1' and a.COLUMN_NAME NOT IN(SELECT b.COLUMN_NAME from information_schema.`COLUMNS` b where b.TABLE_SCHEMA='db2' and a.TABLE_SCHEMA='db1'
and a.TABLE_NAME=b.TABLE_NAME );

select a.TABLE_SCHEMA,a.TABLE_NAME,a.COLUMN_NAME,a.DATA_TYPE,a.COLUMN_DEFAULT
from information_schema.`COLUMNS` a 
where a.TABLE_SCHEMA='db2' and a.COLUMN_NAME NOT IN(SELECT b.COLUMN_NAME from information_schema.`COLUMNS` b where b.TABLE_SCHEMA='db1' and a.TABLE_SCHEMA='db2'
and a.TABLE_NAME=b.TABLE_NAME );

####mysql没有full jion所以变相的多做了一次select查询，这种方法性能比较差,对于表比较多的数据库建议使用上面的分开查询
select b.TABLE_SCHEMA,b.TABLE_NAME,b.COLUMN_NAME,b.DATA_TYPE,c.TABLE_SCHEMA,c.TABLE_NAME,c.COLUMN_NAME,c.DATA_TYPE from 
(select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,DATA_TYPE from information_schema.`COLUMNS` a where a.TABLE_SCHEMA in('db2','db1') )a left join
(select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,DATA_TYPE from information_schema.`COLUMNS` a where a.TABLE_SCHEMA in('db2')) b  on a.TABLE_NAME=b.TABLE_NAME AND a.COLUMN_NAME=b.COLUMN_NAME left join 
(select TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME,DATA_TYPE from information_schema.`COLUMNS` a where a.TABLE_SCHEMA in('db1')) c on a.TABLE_NAME=c.TABLE_NAME AND a.COLUMN_NAME=c.COLUMN_NAME
where b.COLUMN_NAME is null or c.COLUMN_NAME is null ;

#######################################################################################################################
##判断两个数据库互相不存在的表
select a.TABLE_SCHEMA,a.TABLE_NAME
from information_schema.TABLES a 
where a.TABLE_SCHEMA='db1' and a.TABLE_NAME NOT IN(SELECT b.TABLE_NAME from information_schema.TABLES b where b.TABLE_SCHEMA='db2');

select a.TABLE_SCHEMA,a.TABLE_NAME
from information_schema.TABLES a 
where a.TABLE_SCHEMA='db2' and a.TABLE_NAME NOT IN(SELECT b.TABLE_NAME from information_schema.TABLES b where b.TABLE_SCHEMA='db1');


select b.TABLE_SCHEMA,b.TABLE_NAME,c.TABLE_SCHEMA,c.TABLE_NAME from 
(select TABLE_SCHEMA,TABLE_NAME from information_schema.TABLES a where a.TABLE_SCHEMA in('db2','db1') )a left join
(select TABLE_SCHEMA,TABLE_NAME from information_schema.TABLES a where a.TABLE_SCHEMA in('db2')) b  on a.TABLE_NAME=b.TABLE_NAME left join 
(select TABLE_SCHEMA,TABLE_NAME from information_schema.TABLES a where a.TABLE_SCHEMA in('db1')) c on a.TABLE_NAME=c.TABLE_NAME 
where b.TABLE_NAME is null or c.TABLE_NAME is null ;

　　摘自 https://www.cnblogs.com/chenmh/p/5447205.html