經典練習：
四張表：學生表 、老師表、課程表、成績表

學生表 ：

CREATE TABLE `student` (
  `student_number` int(10) NOT NULL AUTO_INCREMENT COMMENT '學生學號',
  `student_name` varchar(50) NOT NULL COMMENT '學生姓名',
  `student_age` int(10) NOT NULL COMMENT '學生年齡',
  `student_sex` varchar(10) NOT NULL COMMENT '學生性別',
  PRIMARY KEY (`student_number`
 
)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

老師表：

CREATE TABLE `teacher` (
  `teacher_number` int(10) NOT NULL COMMENT '教師編號',
  `teacher_name` varchar(10) NOT NULL COMMENT '教師姓名',
  PRIMARY KEY (`teacher_number`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

課程表：

CREATE TABLE `course`
 
 (
  `course_number` int(10) NOT NULL COMMENT '課程編號',
  `course_name` varchar(10) NOT NULL COMMENT '課程名稱',
  `teacher_number` varchar(10) NOT NULL COMMENT '教師編號',
  PRIMARY KEY (`course_number`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

成績表：

CREATE TABLE `student_score` (
  `student_number` int(10) NOT
 
 NULL COMMENT '學生學號',
  `course_number` int(10) NOT NULL COMMENT '課程編號',
  `score` int(10) NOT NULL COMMENT '成績',
  PRIMARY KEY (`student_number`,`course_number`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

裡面資料自己新增！

sql練習：

1、查詢“1”課程比“2”課程成績高的所有學生的學號;

select a.student_number from (select student_number,score from student_score where course_number='1') a,(select student_number,score from student_score where course_number='2') b where a.score>b.score and a.student_number=b.student_number;

2、查詢平均成績大於60分的同學的學號和平均成績;

SELECT student_number,AVG(score) FROM student_score  GROUP BY student_number HAVING AVG(score) > 60

3、查詢所有同學的學號、姓名、選課數、總成績;

SELECT a.student_number,a.student_name,count(c.course_number),sum(score) FROM student a LEFT OUTER JOIN student_score c ON a.student_number=c.student_number GROUP BY a.student_number

4、查詢姓“李”的老師的個數;

SELECT COUNT(t.teacher_name)  from teacher t where teacher_name LIKE '李%'

5、查詢沒學過 “張三” 老師課的同學的學號、姓名

SELECT
    a.student_number,
    a.student_name
FROM
    student a
WHERE
    a.student_number NOT IN(
        SELECT DISTINCT
            (b.student_number)
        FROM
            student_score b,
            course c,
            teacher d
        WHERE
            b.course_number = c.course_number
        AND d.teacher_number = c.teacher_number
        AND d.teacher_name = '張三'
    )

6、查詢學過“001”並且也學過編號“002”課程的同學的學號、姓名;