一、查询某字段不为空mysql
//不为空 SELECT * FROM `table_name` WHERE `col` IS NOT NULL //为空 SELECT * FROM `table_name` WHERE `col` IS NULL
二、mysql中查询一个字段具体是属于哪个数据库的那一张表sql
//其中 table_schema 是所在库, table_name 是所在表 SELECT table_schema,table_name FROM information_schema.columns WHERE column_name = '字段名'