查询数据库中库名称：desc information_schema.schemata;
select distinct schema_name from schemata;查询库中该表的内部信息
desc information_schema.columns;查询该表的所有列：
desc information_schema.columns;
select distinct table_schema from information_schema.columns;COLUMNS表查询所有数据库名称：
select distinct column_name from information_schema.columns;查询当前数据库所有列
select distinct table_schema from information_schema.tables;查询所有表名
select distinct table_name from information_schema.tables;查询表的信息特别注意table_schema和table_name这两个表
