基本语法
Select 字段1、字段2、字段3……from表where条件
查询语句
关键字:select
用法:
查询所有:Select * from 表名 例:Select * from stuInfo
查询部分字段:Select stuName,stuSex from stuInfo
去重复行
关键字:distinct
用法:select distinct 列名1 from 表名 例:Select distinct depart from teacher
注意:distinct必须写在所有列前面
区间语句
关键字:between
用法:Select * from score where degree between 60 and 80
指定条件语句:
关键字:in
用法:Select * from score where degree in (80,85,90)
and语句:
关键字:and
用法:Select * from score where degree>=60 and degree<=80
or语句:
关键字:or
用法:Select * from score where degree>=80 or sex='女'
排序语句:
关键字:order by
用法:Select * from student order by class desc
注:asc(升序,默认),desc(降序)
汇总语句:
关键字:count(*)
题目:查询95031班的学生人数
解题:select count(*) ad CNT from student where class='95031'
求一列的最大(小)值:
关键字:max/min(字段名)
题目:查取score表中的最高(低)分
解题:select max/min(degree) from score
求平均值:
关键字:avg(字段名)
题目:查询‘3-105’号课程的平均分
解题:select avg(degree) as degreeAvg from score where cno='3-105'
分组语句(having 是条件):
关键字:group by(字段名) having 条件
题目:查询score表中至少有5名学生选修课是以‘3’开头的,平均分数
解题:select avg(degree) ad degreeAvg from score where cno like '3%' group by cno having count(*) 5