MySQL学习

查询数据：查询所有列 SELECT * FROM student;查询指定列：SELECT id,NAME,gender FROM student;查询时添加常量列：SELECT id,NAME,gender,age,'java就业班' AS '年级'  FROM student;查询时合并列：SELECT id,(NAME+servlet) FROM student;查询时去除重复记录：SELECT DISTINCT gender FROM student;条件查询：SELECT * FROM student WHERE address IS NULL ;聚合查询：常用的聚合函数： sum()  avg()  max()  min()  count()，分页查询：分页查询当前页的数据的sql: SELECT * FROM student LIMIT (当前页-1)*每页显示多少条,每页显示多少条，查询排序：SELECT * FROM student;分组查询：SELECT gender,COUNT(*) FROM student GROUP BY gender;分组查询后筛选：SELECT gender,COUNT(*) FROM student GROUP BY gender HAVING COUNT(*)>2;