T-SQL 练习整理

收集一些SQL题作为练习，题目来源于网络，答案自己写或者网络，留记录，非标准。

题目

1。表 ExamGrade(ID,CLASS,USERNAME,SUBJECT,Grade), 统计每个班总的考试人数，考语文的人数和总分。

    生成表如下

IF OBJECT_ID('ExamGrade') IS NOT NULL

   DROP TABLE ExamGrade;



CREATE TABLE ExamGrade(

  ID             INT IDENTITY(1,1),

  Class         NVARCHAR(20),

  UserName  NVARCHAR(20),

  Subjects     NVARCHAR(20),

  Grade        INT

);

GO



INSERT INTO ExamGrade(Class,UserName,Subjects,Grade)

SELECT 'Class1','Lily','Math',90

UNION ALL

SELECT 'Class1','Lily','Chinese',89

UNION ALL

SELECT 'Class1','Tom','Math',26

UNION ALL

SELECT 'Class1','Tom','Chinese',31

UNION ALL

SELECT 'Class2','Lucy','Math',90

UNION ALL

SELECT 'Class2','Lucy','Chinese',80

UNION ALL

SELECT 'Class2','Jerry','Math',70

;

GO

View Code

分析

要求中有分别统计班级的结果会用到 GRGOUP BY，既有整体统计又有分科统计，会用到表与表之间的JOIN。

解答

SELECT S.Class AS Class,SUM(Grade) AS SumGrade, COUNT(DISTINCT UserName) AS SumStuAttendExam, SumStuAttendChsExam

FROM ExamGrade AS S

LEFT JOIN

(SELECT Class, COUNT(UserName) AS SumStuAttendChsExam

 FROM ExamGrade

 WHERE Subjects = 'Chinese'

 GROUP BY Class

) AS P

ON S.Class=P.Class

GROUP BY S.Class,SumStuAttendChsExam

ORDER BY S.Class;

GO

结果