select count(1) from information_schema.columns where table_schema = "testdatabase" and table_name ='testtable'
//查看某个数据库中某个表有多少字段

select count(1) from information_schema.columns where table_schema = "testdatabase"  
//查看某个数据库中整体有多少字段


select count(1) , table_schema from information_schema.tables where table_schema ='testdatabase'
//查看某个数据库中有多少表

select count(1) , table_schema from information_schema.tables group by table_schema
//查看所有的数据库中各有多少表