SQL——EXISTS子查询

–任务1 : 査询选修某课程的学生倍息
–查询选修课程编号为"0101001"课程的学生的学号和姓名
–方法一：连接查询（内连接），分析数据源（单表、多表）

SELECT *
FROM Student,Result WHERE Student.Sno=Result.sno
SELECT *
FROM Student INNER JOIN Result
ON Student .Sno=Result.sno

–方法二：IN子查询，从已知条件（课程编号0101001）去查询有关学生的信息
–适合内部表（子表）记录较少的情况

SELECT *
FROM Result
WHERE cno='0101001'

SELECT *
FROM Student
WHERE Sno IN ('1201011101','1201011102','1201011103')

SELECT *
FROM Student
WHERE Sno IN(
	SELECT Sno
	FROM Result
	WHERE cno='0101001')
--EXISTS子查询，适合外部表（父表）记录较少的情况
SELECT *
FROM Student
WHERE EXISTS(
	SELECT *
	FROM Result
	WHERE cno='0101001' AND Student.Sno=Result.Sno )