有你，查询数据我什么都不怕。快快掌握！！
出大招的工具：
1.使用LIKE、BETWEEN、IN进行模糊查询
eg1:
SELECT * FROM Students
WHERE 姓名 like ‘张%‘
eg2:
SELECT StudentID, Score FROM SCore WHERE Score
BETWEEN 60 AND 80
eg3:
SELECT SName AS 学生姓名,SAddress AS 地址
FROM Students
WHERE SAddress IN (‘北京‘,‘广州‘,‘上海‘)
2.通配符
eg:
SELECT * FROM 数据表
WHERE 编号 LIKE ‘00[^8]%[AC]%‘
3.SUM()
AVG()
MAX()、MIN()
COUNT()
eg1:
SELECT SUM(Score) AS 学号为23的学生总分
FROM Score
WHERE StudentID =23
eg2:
SELECT AVG(SCore) AS 及格平均成绩
FROM Score
WHERE Score >=60
eg3:
SELECT AVG(SCore) AS 平均成绩, MAX (Score) AS 最高分,
MIN (Score) AS 最低分
FROM Score
WHERE Score >=60
eg4:
SELECT COUNT (*) AS 及格人数
FROM Score
WHERE Score>=60
4.分组查询用法
SELECT …… FROM <表名>
WHERE ……
GROUP BY ……
eg:
SELECT COUNT(*) AS 人数, SGrade AS 年级
FROM Students
GROUP BY SGrade
eg2:
SELECT CourseID, AVG(Score) AS 课程平均成绩
FROM Score
GROUP BY CourseID
eg3:
SELECT CourseID, AVG(Score) AS 课程平均成绩
FROM Score
GROUP BY CourseID
ORDER BY AVG(Score)
5.多列分组
SELECT COUNT(*) AS 人数,SGrade AS 年级,SSex AS 性别
FROM StudentS
GROUP BY SGrade,SSex
ORDER BY SGrade
6.分组筛选
SELECT …… FROM <表名>
WHERE ……
GROUP BY ……
HAVING……
eg:
SELECT COUNT(*) AS 人数,SGrade AS 年级
FROM Students
GROUP BY SGrade
HAVING COUNT(*)>15
7.多表连接查询
内连接(INNER JOIN)
SELECT ……
FROM 表1
INNER JOIN 表2
ON ……
等价于
SELECT ……
FROM 表1，表2
WHERE ……
eg:
SELECT Students.SName, Score.CourseID, Score.Score
FROM Students,Score
WHERE Students.SCode = Score.StudentID
三表内连接：
eg：
SELECT
S.SName AS 姓名, CS.CourseName AS 课程, C.Score AS 成绩
FROM Students AS S
INNER JOIN Score AS C ON (S.SCode = C.StudentID)
INNER JOIN Course AS CS ON (CS.CourseID = C.CourseID)
外连接
左外连接 (LEFT JOIN)
eg：
SELECT S.SName,C.CourseID,C.Score
FROM Students AS S
LEFT JOIN Score AS C
ON C.StudentID = S.SCode
右外连接 (RIGHT JOIN)
eg：
SELECT 图书编号,图书名称,出版社名称
FROM 图书表
RIGHT OUTER JOIN 出版社表
ON 图书表.出版社编号 = 出版社表.出版社编号