查询MySql数据库架构信息：数据库，表，表字段

/*1.查询所有数据库*/
show databases;

/*2.查询所有数据表*/
select * from information_schema.tables where table_schema='world'

/*3.查询指定表的所有字段*/
select * from information_schema.columns
where table_schema='world'
and table_name='city'