通配符：
_ 单个字符 %任意字符 []范围内的字符 [^]范围外的字符
SELECT * FROM Student
UPDATE Student SET StudentName='王波' WHERE StudentNo='Y21003011'
--模糊查询：查询学生表中姓’冯‘的学生记录
SELECT * FROM Student WHERE StudentName LIKE '王_'
SELECT * FROM Result WHERE SubjectId LIKE '[1-9]'
SELECT * FROM Result WHERE SubjectId LIKE '[^1-3]'
--查询空的数据行
SELECT * FROM Student WHERE Email=''
--查询区间内数据:BETWEEN AND
SELECT * FROM Result WHERE SubjectId BETWEEN 1 AND 10
--查询与列所匹配值相同的数据：IN
SELECT * FROM Student WHERE Address IN ('新疆乌鲁木齐','北京市海淀区五道口北大青鸟IT职业技术学院','黑龙江哈尔滨')
--聚合函数
--1.求和：SUM()
SELECT SUM(StudentResult) AS '总成绩',Result.SubjectId FROM Result WHERE SubjectId=3
--2.平均值
SELECT AVG(StudentResult) AS '平均成绩' FROM Result
--3.最大值，最小值
SELECT MAX(StudentResult) AS '最高成绩' FROM Result
SELECT MIN(StudentResult) AS '最低成绩' FROM Result
--4.统计记录数:COUNT(*)和COUNT(1)的区别
SELECT COUNT(StudentNo) AS '记录数' FROM Result
一般情况下select count(*) 与select count(1)两者返回的结果一致。
但是针对表中主键的有无，情况会有不同。
无主键：count(1)比count(x)快
有主键：count(主键)最快
count(*)与count(1)都包括null统计，而count(column)不包括null统计
