模糊查询于聚合函数

Posted 2021-01-28 whtt

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