查询所有数据库下记录条数

select SUM(TABLE_ROWS) from information_schema.tables where TABLE_TYPE = 'BASE TABLE';

要查询表所占的容量，就是把表的数据和索引加起来就可以了

select CONCAT(round((sum(DATA_LENGTH)+sum(INDEX_LENGTH))/1024/1024, 2), 'M') from information_schema.tables 
where TABLE_TYPE = 'BASE TABLE';

查询所有的数据大小

select concat(round(sum(DATA_LENGTH/1024/1024),2),'M') from information_schema.tables where TABLE_TYPE = 'BASE TABLE'; 

oracle的请参考链接：

https://www.jianshu.com/p/411f5ca6f341